Nano porous alumina, preparation method and application thereof, and lithium ion battery diaphragm

Abstract

The invention discloses nano-porous aluminum oxide, a preparation method and application thereof and a lithium ion battery diaphragm, and relates to the technical field of battery materials. The crystal form of the nano-porous aluminum oxide comprises the following components in percentage by volume: 30-100% of theta phase and 0-70% of delta phase. In the nano-porous aluminum oxide, the volume of fine pores with the pore diameter of 10-75nm is 0.05-0.15 cm < 3 > / g. By controlling the crystalline phase composition and the pore volume of the nano-porous aluminum oxide, the nano-porous aluminum oxide can be ensured to have excellent puncture resistance and heat resistance while having high liquid absorption rate, and the application of the nano-porous aluminum oxide in the ultrathin coating is realized. Meanwhile, the nano-porous aluminum oxide provided by the invention can be directly prepared into a crystal structure with a theta phase and a delta phase, the pore volume range of the nano-porous aluminum oxide is controlled, the prepared nano-porous aluminum oxide does not need to be screened, graded and compounded, and the technological process of the nano-porous aluminum oxide is greatly simplified.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a kind of nano-porous alumina and its preparation method and application, lithium ion battery separator. BACKGROUND

[0002] As one of the most important energy storage technologies today, lithium ion batteries have been widely used in consumer electronics, electric vehicles and energy storage systems, etc. As a core component of lithium ion batteries, electrolyte transports lithium ions between the positive and negative electrodes, and its performance directly affects the energy density, cycle life and safety performance of the battery. In recent years, with the continuous improvement of battery performance requirements, the research of electrolyte system has become one of the key directions of battery technology development.

[0003] During the operation of the battery, the electrolyte will undergo complex interfacial reactions with the electrode material, including decomposition, oxidation and other side reactions, which will gradually consume the electrolyte. This consumption not only reduces the number of active lithium ions, but also forms a non-conductive interfacial layer on the electrode surface, increasing the internal resistance of the battery, thereby significantly affecting the capacity retention rate and cycle stability of the battery. Especially under harsh working conditions such as high voltage, high temperature or fast charging and discharging, the decomposition and consumption of electrolyte are more serious, which has become one of the main bottlenecks restricting the improvement of battery performance.

[0004] To improve the wettability and retention performance of electrolyte in the battery, researchers have developed a variety of functional coating technologies. Among them, porous alumina is widely used in the surface modification of separators and electrodes due to its excellent electrochemical stability, thermal stability and high specific surface area. By constructing a suitable pore structure in the porous alumina coating, the wettability and retention capacity of the electrolyte can be significantly improved, and more channels for lithium ion transport can be provided. This technology not only prolongs the service life of the electrolyte, but also continuously replenishes the electrolyte during the battery cycle, thereby effectively alleviating the performance degradation problem of the battery.

[0005] However, the porous alumina materials in the prior art still have some limitations. First, the pore size distribution and pore volume of conventional porous alumina often cannot meet the needs of fast wettability and long-term retention of electrolyte. Second, in the application of ultra-thin coating, the mechanical strength and puncture resistance of existing materials need to be improved. In addition, in high temperature working environment, the thermal stability of traditional porous alumina coating still needs to be improved. These technical bottlenecks limit the application effect of porous alumina in improving battery performance.

[0006] In view of this, the present application is proposed. SUMMARY

[0007] The present application relates to the technical field of battery materials, in particular to a kind of nano-porous alumina and its preparation method and application, lithium ion battery separator.

[0008] The present application is implemented as follows: In a first aspect, the present application provides a nanoporous alumina, wherein the crystal phase of the nanoporous alumina comprises 30-100% of theta phase and 0-70% of delta phase in terms of volume percentage.

[0009] In the nanoporous alumina, the volume of the fine pores with a pore size of 10-75 nm is 0.05-0.15 cm 3 / g.

[0010] In a second aspect, the present application provides a preparation method of the nanoporous alumina as in any of the preceding embodiments, comprising mixing an aluminum salt, a crystal grain inhibitor, a pore-forming agent and water to perform a hydrothermal reaction, obtaining a nanoporous alumina precursor slurry, and drying the nanoporous alumina precursor slurry into a nanoporous alumina precursor powder and then performing calcination.

[0011] In a third aspect, the present application provides a lithium ion battery separator, comprising a separator body and a nanoporous alumina coating layer coated on at least one side surface of the separator body, wherein the raw material of the nanoporous alumina coating layer comprises the nanoporous alumina as in any of the preceding embodiments or the nanoporous alumina prepared by the preparation method as in any of the preceding embodiments.

[0012] In a fourth aspect, the present application provides an application of the nanoporous alumina as in any of the preceding embodiments or the nanoporous alumina prepared by the preparation method as in any of the preceding embodiments in the field of batteries.

[0013] The present application has the following beneficial effects: The present application provides a nanoporous alumina, a preparation method and an application thereof, and a lithium ion battery separator. By controlling the crystal phase composition of the nanoporous alumina and the volume of the fine pores with a pore size of 10-75 nm in the nanoporous alumina, the nanoporous alumina can have excellent puncture resistance and heat resistance while having a high liquid absorption rate, and the application of the nanoporous alumina in an ultrathin coating layer is realized. The nanoporous alumina provided by the present application can directly obtain a crystal structure with theta phase and delta phase and control the pore volume range, without the need for screening, grading and compounding of the prepared nanoporous alumina, thereby greatly simplifying the process flow of the nanoporous alumina. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturers are used. If the reagents or instruments used are not specified by the manufacturers, they are all conventional products that can be purchased on the market.

[0015] The features and performances of the present application are further described in detail below in combination with embodiments.

[0016] In a first aspect, the present application provides a nano-porous alumina, the crystal form of the nano-porous alumina includes 30-100% theta phase and 0-70% delta phase in terms of volume percentage.

[0017] By controlling the crystal phase organization of the nano-porous alumina, the theta phase alumina has excellent thermal stability and mechanical strength, which is one of the key factors to achieve high-temperature resistance and puncture resistance; the delta phase alumina improves the ductility of the material to some extent, which helps to avoid brittle fracture of the pore wall. By controlling the crystal form ratio of the two, the nano-porous alumina can have good thermal stability and structural stability, and on this basis, the wettability and liquid retention capacity of the nano-porous alumina to the electrolyte can be further optimized, and the nano-porous alumina with better comprehensive performance can be obtained.

[0018] Further preferably, the crystal form of the nano-porous alumina includes 45-100% theta phase and 0-45% delta phase in terms of volume percentage. By increasing the proportion of theta phase, the structural stability of the nano-porous alumina can be further improved.

[0019] It should be noted that the crystal form of the nano-porous alumina and its ratio are obtained by X-ray diffractometer test.

[0020] Currently, some nano-porous aluminas contain gamma phase, which can improve the pore volume of the nano-porous alumina, but its thermal stability is poor, and the prepared coating is easy to soften or shrink, causing the end products such as batteries to be defective. The nano-porous alumina provided by the present application is composed of theta phase and delta phase, and the nano-porous alumina obtained has good structural stability and good thermal stability.

[0021] Specifically, in the nano-porous alumina, the fine pore volume within a pore size range of 10-75 nm is 0.05-0.15 cm 3 / g.

[0022] In the electrolyte, the size of the solvated lithium ion is about 5 nm, therefore, in order to improve the ionic conductivity of the lithium battery, the nano-porous alumina needs to provide a large number of ion channels >5 nm to facilitate the transmission of the solvated lithium ion. By controlling the fine pore volume of the nano-porous alumina within a pore size range of 10-75 nm, the wettability and liquid retention capacity of the nano-porous alumina to the electrolyte can be improved.

[0023] When the pore size range is lower than 10 nm, the lithium ion transmission process is limited, affecting the electrochemical performance of the battery; when the pore size range is higher than 75 nm, it may cause the nano-porous alumina to have poor structural stability, therefore, the fine pore volume of the nano-porous alumina within a pore size range of 10-75 nm is controlled to meet 0.05-0.15 cm 3 / g, and a nano-porous alumina material with better comprehensive performance can be obtained.

[0024] When the pore volume of the pores with a pore size of 10-75 nm is less than 0.05 cm 3 / g, the alumina particles in the nano-porous alumina coating formed by the nano-porous alumina are tightly packed, the thermal expansion of the particles is limited at high temperatures, the internal stress cannot be released through the pores, and the heat resistance is reduced; when the pore volume of the pores with a pore size of 10-75 nm is greater than 0.15 cm 3 / g, the internal pores of the alumina particles are too many, and when the battery is squeezed or impacted by burrs, the pore edges of the alumina particles are easy to cause micro-cracks and quickly expand, eventually leading to the overall rupture of the separator and the reduction of the puncture resistance of the material.

[0025] In an optional embodiment, the pore volume of the nano-porous alumina is 0.1-0.3 cm 3 / g. By controlling the pore volume of the nano-porous alumina within the above range, the nano-porous alumina has high liquid absorption rate and excellent structural stability, ensuring good puncture resistance. When the pore volume of the nano-porous alumina is less than 0.1 cm 3 / g, the liquid absorption and storage capacity of the nano-porous alumina are reduced; when the pore volume of the nano-porous alumina is greater than 0.3 cm 3 / g, the viscosity of the slurry prepared from the nano-porous alumina is too high, and the slurry cannot be fully dispersed for coating.

[0026] Preferably, the mass percentage of the single-crystal particles in the nano-porous alumina is 90% or more, which helps to improve the heat shrinkage resistance of the separator; the uniformity of the single-crystal particle structure also helps to reduce the interface impedance and improve the electrochemical performance of the battery.

[0027] Preferably, the size of the single-crystal particles is 30-100 nm. When the particle size of the single-crystal particles is less than 30 nm, the viscosity of the slurry prepared from the nano-porous alumina is high, and the slurry cannot be fully dispersed, increasing the difficulty of coating; when the particle size of the single-crystal particles is greater than 100 nm, the heat shrinkage rate and the puncture resistance of the separator with the nano-porous alumina coating are significantly reduced.

[0028] It should be noted that the crystal phase composition and pore structure of the nanoporous alumina are closely related to the preparation process, and the existing preparation process of the nanoporous alumina is difficult to control the process precision, so that the prepared nanoporous alumina can be directly applied to the nanoporous alumina coating. Therefore, usually after the nanoporous alumina is prepared, the final raw material for preparing the nanoporous alumina coating is obtained by screening, grading and compounding, which is a complicated process and the nanoporous alumina is wasted. The preparation method of the nanoporous alumina provided by the present application can directly obtain the nanoporous alumina raw material meeting the application of the nanoporous alumina coating, and has better industrial application value.

[0029] In a second aspect, the present application provides a preparation method of the nanoporous alumina as in the preceding embodiments, comprising mixing an aluminum salt, a grain inhibitor, a pore former and water to perform a hydrothermal reaction, obtaining a nanoporous alumina precursor slurry, and drying the nanoporous alumina precursor slurry into a nanoporous alumina precursor powder and then calcining.

[0030] By mixing the aluminum salt, the grain inhibitor, the pore former and the water to perform the hydrothermal reaction, a nanoparticle precursor is obtained, so that a nanoporous structure is obtained, and a nanoporous alumina with a porous structure is obtained through a subsequent calcination process. The nanoporous alumina has high liquid absorption rate, puncture resistance and heat resistance by improving the pore volume under ultra-thin coating, and can achieve very good effect when used in diaphragm coating.

[0031] In some preferred embodiments of the present application, the preparation method of the nanoporous alumina comprises the following steps: S01, mixing In an optional embodiment, the aluminum salt, the grain inhibitor, the pore former and the water are mixed by sand milling, and the mixing time is 1-5h, to obtain an aluminum salt slurry. The sand milling is used to fully disperse the aluminum salt, the grain inhibitor and the pore former, which is beneficial to the subsequent reaction to generate a nanoporous alumina with a pore structure and a crystal structure meeting the requirements.

[0032] In an optional embodiment, the grain inhibitor comprises at least one of sodium hydroxide, sodium polyacrylate, potassium hydroxide and ammonia water, and is more preferably ammonia water.

[0033] Preferably, the mass of the grain inhibitor is 0.005-0.2% of the mass of the aluminum salt, for example, it can be any one of 0.005%, 0.01%, 0.05%, 0.1%, 0.15% or 0.2% or a range value composed of any two of them.

[0034] By controlling the addition amount of the grain inhibitor and the selection of raw materials, the abnormal growth of the nanoporous alumina grain during the hydrothermal and calcination processes can be inhibited, which is helpful to obtain a nanoporous structure with uniform particle size and small grain size.

[0035] Preferably, the pore-forming agent comprises a triquaternary ammonium and / or a trimethyl ammonium, more preferably a triquaternary ammonium.

[0036] Preferably, the mass of the pore-forming agent is 0.01-2% of the mass of the aluminum salt, for example, can be any of 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5% or 2% or a range value consisting of any two of them.

[0037] By controlling the amount of pore-forming agent added and the selection of raw materials, a controllable nano-pore channel structure can be formed in the aluminum salt, while avoiding excessive porosity leading to a decrease in material strength, and also avoiding too few pores affecting the liquid absorption rate and electrolyte wettability.

[0038] Preferably, the aluminum salt comprises at least one of aluminum hydroxide, pseudo-boehmite and aluminum chloride, more preferably pseudo-boehmite.

[0039] Preferably, the mass ratio of the aluminum salt to water is 0.5:9.5-2:8.

[0040] By controlling the selection of the aluminum salt and the mass ratio to water, it can be ensured that the raw materials in the aluminum salt slurry are fully dispersed. In addition, by controlling the above-mentioned selection of raw materials and the ratio of raw materials of the aluminum salt, the grain inhibitor and the pore-forming agent, while ensuring that the nano-porous alumina has excellent pore channel performance and crystal phase structure, the grain inhibitor and the pore-forming agent will not produce impurities during the reaction process and are easy to remove.

[0041] Preferably, the sand mill uses a horizontal sand mill, and the water is pure water.

[0042] S02, hydrothermal reaction In an optional embodiment, the aluminum salt slurry obtained in S01 is placed in a hydrothermal reaction kettle for hydrothermal reaction to obtain a nano-porous alumina precursor slurry.

[0043] In an optional embodiment, the temperature of the hydrothermal reaction is 130-240°C, the reaction time is 6-50h, and the pressure of the reaction cavity is 1.5-3MPa.

[0044] Preferably, the temperature of the hydrothermal reaction is 170-220°C, and the reaction time is 9-30h.

[0045] By controlling the parameters of the hydrothermal reaction within the above-mentioned range, it is beneficial to ensure the thermal stability, puncture strength and liquid absorption rate of the nano-porous alumina. For example, too high or too low hydrothermal reaction temperature will result in a decrease in the thermal stability and puncture strength of the nano-porous alumina.

[0046] S03, drying In an optional embodiment, the drying comprises spray drying the nanoporous alumina precursor slurry obtained in S02 after concentration, to obtain nanoporous alumina precursor powder.

[0047] Preferably, the solid content of the obtained nanoporous alumina precursor concentrate is greater than 30%.

[0048] Preferably, the water content of the obtained nanoporous alumina precursor powder is less than or equal to 0.3%.

[0049] S04, calcination The nanoporous alumina precursor powder obtained in S03 is placed in a crucible for calcination, to obtain nanoporous alumina agglomerates.

[0050] In an optional embodiment, the parameters of the calcination include: a heating rate of 1-10°C / min, a holding temperature of 600-1100°C, and a holding time of 0.5-10h; and the loading amount of the nanoporous alumina precursor powder is greater than or equal to 80% of the volume of the crucible.

[0051] Preferably, the heating rate of the calcination is 4-6°C / min, and the holding temperature is 800-1100°C.

[0052] By controlling the parameters of the calcination within the above ranges, a large amount of pore-forming agents are contained in the crystal lattices of the nanoporous alumina precursor powder. With the control of the furnace temperature of the calcination furnace, the heat energy is transferred from the surface of the powder to the center of the powder, and the pore-forming agents in the powder volatilize to form channels in the nanoporous alumina particles.

[0053] Preferably, the calcination can be performed in stages to ensure the morphology and structure of the nanoporous alumina particles.

[0054] S05, post-treatment In an optional embodiment, the nanoporous alumina agglomerates obtained after the calcination are subjected to sand mill dispersion to obtain a nanoporous alumina slurry. Preferably, pure water is used as the dispersant for the sand mill dispersion.

[0055] In order to meet the use requirements of different manufacturers for nanoporous alumina, for example, the processes of some manufacturers are suitable for water-based slurries, and therefore the nanoporous alumina slurry obtained by the above sand mill dispersion can be directly sold as a product; or the nanoporous alumina slurry is concentrated by ceramic membrane and then sold as a product.

[0056] The processes of other manufacturers are suitable for oil-based slurries, and therefore the nanoporous alumina slurry obtained by the above sand mill dispersion needs to be dried and then sold in the form of powder. For example, the nanoporous alumina slurry is directly spray dried to obtain nanoporous alumina powder, or the nanoporous alumina slurry is concentrated by ceramic membrane and then spray dried to obtain nanoporous alumina powder.

[0057] In a third aspect, the present application provides a lithium ion battery separator, comprising a separator body and a nano-porous alumina coating coated on at least one side surface of the separator body, wherein the raw material of the nano-porous alumina coating comprises the nano-porous alumina according to any one of the preceding embodiments or prepared by the preparation method according to any one of the preceding embodiments.

[0058] It should be noted that the specific use method of the nano-porous alumina provided by the present application in the separator can be carried out by using the existing process, and the present application does not limit this.

[0059] Alternatively, the nano-porous alumina prepared by the present application can also be used in combination with other substances that can be used in the separator, and the present application is applicable to the solutions that can be known by the person skilled in the art within a reasonable range.

[0060] Alternatively, after the nano-porous alumina prepared by the present application is prepared into a nano-porous alumina slurry, the separator slurry formula does not need to be modified, and the nano-porous alumina can be obtained by using conventional coating means.

[0061] In a fourth aspect, the present application provides the nano-porous alumina according to any one of the preceding embodiments or prepared by the preparation method according to any one of the preceding embodiments for use in the field of batteries.

[0062] For example, in addition to being used as a coating for a battery separator, the nano-porous alumina provided by the present application can also be used as a coating for an electrode material cladding layer and an electrode material surface coating, and the like, which are various battery components that directly contact an electrolyte.

[0063] Example 1 The present embodiment provides a preparation method of nano-porous alumina, comprising the following steps: S01, mixing 1t pseudo-boehmite, 0.1kg ammonia water, 1kg triquaternary ammonium, and 9t pure water are sand-mixed for 2h to obtain an aluminum salt slurry.

[0064] S02, hydrothermal reaction The aluminum salt slurry obtained in the step S01 is placed in a hydrothermal reaction kettle for hydrothermal reaction, the reaction temperature is 210℃, the reaction time is 9h, and the pressure in the reaction cavity is 1.7MPa, to obtain a nano-porous alumina precursor slurry.

[0065] The particle size of the alumina particles in the nano-porous alumina precursor slurry is 85nm, and the crystalline water content is 13wt%.

[0066] S03, drying The nanoporous alumina precursor slurry obtained in S02 is concentrated to a solid content of 35%, and then spray dried to obtain a nanoporous alumina precursor powder with a water content of 0.27%.

[0067] S04, calcination The nanoporous alumina precursor powder obtained in S03 is placed in a crucible for calcination, the loading amount of the nanoporous alumina precursor powder is 80% of the volume of the crucible, the heating rate is 5°C / min, the holding temperature is 1100°C, and the holding time is 2h, to obtain a nanoporous alumina aggregate.

[0068] The nanoporous alumina aggregate has a particle size of 85nm, a pore volume of 0.181cm 3 / g, and a fine pore volume of 0.097cm 3 / g with a pore size of 10-75nm.

[0069] S05, post-treatment The nanoporous alumina aggregate 1t obtained in S04 is sand-milled and dispersed with pure water 5t to obtain a nanoporous alumina slurry, which is spray dried to obtain a nanoporous alumina powder; or the nanoporous alumina slurry is concentrated by ceramic membrane to obtain a high-solid-content nanoporous alumina slurry.

[0070] Example 2 This example provides a method for preparing nanoporous alumina, and the specific steps are similar to those of Example 1, except that the temperature of the hydrothermal reaction in S02 is 200°C.

[0071] Example 3 This example provides a method for preparing nanoporous alumina, and the specific steps are similar to those of Example 1, except that the temperature of the hydrothermal reaction in S02 is 220°C.

[0072] Example 4 This example provides a method for preparing nanoporous alumina, and the specific steps are similar to those of Example 1, except that the mass of the ammonia water in S01 is 2kg.

[0073] Example 5 This example provides a method for preparing nanoporous alumina, and the specific steps are similar to those of Example 1, except that the mass of the ammonia water in S01 is 50g.

[0074] Example 6 This example provides a method for preparing nanoporous alumina, and the specific steps are similar to those of Example 1, except that the calcination temperature in S04 is 1000°C.

[0075] Example 7 This example provides a method for preparing nanoporous alumina, and the specific steps are similar to those of Example 1, except that the calcination temperature in the S04 step is 800°C.

[0076] Example 8 This example provides a method for preparing nanoporous alumina, and the specific steps are similar to those of Example 1, except that the mass of the quaternary ammonium salt in the S01 step is 20 kg.

[0077] Example 9 This example provides a method for preparing nanoporous alumina, and the specific steps are similar to those of Example 1, except that the mass of the quaternary ammonium salt in the S01 step is 5 kg.

[0078] Example 10 This example provides a method for preparing nanoporous alumina, and the specific steps are similar to those of Example 1, except that the mass of the quaternary ammonium salt in the S01 step is 1 kg.

[0079] Comparative Example 1 This comparative example provides a method for preparing nanoporous alumina, and the specific steps are similar to those of Example 1, except that no ammonia water is added in the S01 step.

[0080] Comparative Example 2 This comparative example provides a method for preparing nanoporous alumina, and the specific steps are similar to those of Example 1, except that no quaternary ammonium salt is added in the S01 step.

[0081] Comparative Example 3 This comparative example provides a method for preparing nanoporous alumina, and the specific steps are similar to those of Example 1, except that the temperature of the hydrothermal reaction in the S02 step is 250°C.

[0082] Comparative Example 4 This comparative example provides a method for preparing nanoporous alumina, and the specific steps are similar to those of Example 1, except that the temperature of the hydrothermal reaction in the S02 step is 120°C.

[0083] Comparative Example 5 This comparative example provides a method for preparing nanoporous alumina, and the specific steps are similar to those of Example 1, except that the calcination temperature in the S04 step is 500°C.

[0084] Comparative Example 6 This comparative example provides a method for preparing nanoporous alumina, and the specific steps are similar to those of Example 1, except that the amount of ammonia water added in the S01 step is 0.3%.

[0085] Comparative Example 7 The comparative example provides a preparation method of nanoporous alumina, and the specific steps are similar to those of Example 1, and the only difference is that the ammonia water addition amount in S01 step is 0.004%.

[0086] Comparative Example 8 The comparative example provides a preparation method of nanoporous alumina, and the specific steps are similar to those of Example 1, and the only difference is that the quaternary ammonium salt addition amount in S01 step is 3%.

[0087] Comparative Example 9 The comparative example provides a preparation method of nanoporous alumina, and the specific steps are similar to those of Example 1, and the only difference is that the quaternary ammonium salt addition amount in S01 step is 0.008%.

[0088] Comparative Example 10 The comparative example provides a preparation method of nanoporous alumina, and the specific steps are similar to those of Example 1, and the only difference is that the hydrothermal reaction time in S02 step is 60h.

[0089] Comparative Example 11 The comparative example provides a preparation method of nanoporous alumina, and the specific steps are similar to those of Example 1, and the only difference is that the calcination holding time in S04 step is 12h.

[0090] The nanoporous alumina prepared by the method of Examples 1-10 and Comparative Examples 1-11 is detected by X-ray diffractometer for crystal phase composition, and the pore volume and fine pore volume of 10-75nm pore size are detected by a micrometer tester, and the results are shown in Table 1.

[0091] Table 1 Crystal phase composition and pore channel parameters of nanoporous alumina

[0092] As can be seen from Table 1, the nanoporous alumina prepared by the method provided in the examples has θ phase, and the pore volume and fine pore volume of the nanoporous alumina are more appropriate.

[0093] Comparative Example 1 does not add grain inhibitors, and the pore volume of the obtained nanoporous alumina is low, and the fine pore volume is also low, so the liquid absorption effect may be affected.

[0094] Comparative Example 2 does not add pore-forming agents, and the pore volume of the obtained nanoporous alumina is low, and the fine pore volume is 0, so the liquid absorption capacity is not good.

[0095] Comparative Example 3 increases the hydrothermal temperature, and the fine pore volume of the obtained nanoporous alumina is large, and the strength may be low.

[0096] The hydrothermal temperature of Comparative Example 4 was reduced, and the pore volume and fine pore volume of the obtained nanoporous alumina were both low, which might affect the liquid absorption effect.

[0097] The calcination temperature of Comparative Example 5 was reduced, and the crystal phase of the obtained nanoporous alumina was γ phase, which might have poor thermal stability.

[0098] The inhibitor of Comparative Example 6 was increased, and the pore volume of the obtained nanoporous alumina was low, and the fine pore volume was also low, which might affect the liquid absorption effect.

[0099] The inhibitor of Comparative Example 7 was reduced, and the pore volume and fine pore volume of the obtained nanoporous alumina were both low, which might affect the liquid absorption effect.

[0100] The pore-forming agent of Comparative Example 8 was increased, and the fine pore volume of the obtained nanoporous alumina was low, which might affect the liquid absorption effect.

[0101] The pore-forming agent of Comparative Example 9 was reduced, and the pore volume of the obtained nanoporous alumina was low, and the fine pore volume was also low, which might affect the liquid absorption effect.

[0102] The hydrothermal holding time of Comparative Example 10 was extended, and the fine pore volume of the obtained nanoporous alumina was low, which might affect the liquid absorption effect.

[0103] The calcination holding time of Comparative Example 11 was extended, and the obtained nanoporous alumina appeared α crystal phase, and the pore volume was low, which might affect the liquid absorption effect.

[0104] Test Example 1 The nanoporous alumina prepared by the method of Examples 1-10 and Comparative Examples 1-11 was used for coating the separator, and a separator sample was obtained. The coating method was the same, the separator substrate was a PE substrate, and the thickness of the nanoporous alumina coating was 1 μm (the coating wire rod size was 1 um, and the actual coating thickness was affected by the size of the beating powder, and the thickest was not more than 1 um). The heat resistance, puncture resistance and liquid absorption rate of the nanoporous alumina coating were tested, and the results are shown in Table 2.

[0105] Among them, the heat resistance test method was: cutting 10 cm x 10 cm separator sample, respectively baking at 130 ℃ for 1 h, baking at 150 ℃ for 30 min, measuring the size change before and after baking, and calculating the thermal shrinkage rate.

[0106] The puncture resistance test method was: GB / T 36363-2018 "Polyolefin separator for lithium ion battery" fixed the separator sample on the clamp, used a steel needle with a diameter of 1.0 mm and a sharp end spherical radius of 0.5 mm, vertically punctured at a speed of (50±5) mm / min or (100±10) mm / min, and recorded the maximum puncture force value.

[0107] The liquid absorption rate test method is as follows: a certain area of the separator sample is cut, the thickness is measured and the volume V1 is calculated; the separator sample is rolled into a cylindrical shape, fixed with a non-liquid absorption ring, and soaked in electrolyte for 10-120 min; the mass change of the separator sample after the electrolyte is drained is measured, and the liquid absorption rate is calculated.

[0108] The test method for coating thickness is as follows: a thickness gauge with a precision of 0.01 μm is used to measure the thickness of the nano-porous alumina coating at multiple points on the separator sample, and the average value is taken.

[0109] Table 2 Properties of nano-porous alumina coating

[0110] As can be seen from Table 2, the nano-porous alumina coating prepared from the nano-porous alumina provided by the embodiments of the present application has a low thermal shrinkage rate (below 2%), a high puncture strength (above 486 gf), a high liquid absorption rate (above 1.8%), and a coating thickness of below 0.5 um. The application of the nano-porous alumina coating in batteries can prolong the service life of the batteries, reduce the weight of the batteries, and improve the electrochemical performance of the batteries.

[0111] The thermal shrinkage rate of Comparative Example 1 is high, the thermal stability is poor, the puncture strength is low, and the actual coating thickness can only reach 0.97 um. Moreover, it is difficult to coat the nano-porous alumina coating uniformly when the coating thickness is further reduced, so it is difficult to adapt to the application scenario of thin coating. In addition, the coating of Comparative Example 1 also has a low liquid absorption rate, which seriously affects its application in batteries. The thermal stability and puncture strength of Comparative Example 2 are both good, but the liquid absorption rate is greatly reduced, which makes it difficult to meet the use requirements of batteries. The thermal stability of Comparative Examples 3 and 4 is poor, and the puncture strength is also low, which makes it difficult to meet the use requirements of batteries. The viscosity of the nano-porous alumina slurry of Comparative Examples 5 and 6 is too high after slurry preparation, and the agglomeration is serious, so it cannot be coated. The coating thickness of Comparative Example 7 is too thick, and the thermal shrinkage rate is high, the thermal stability is poor, and the puncture strength is low. The liquid absorption rate of the coating of Comparative Example 8 is low. The thermal shrinkage rate of Comparative Example 9 is high, the thermal stability is poor, and the puncture strength is low; the coating thickness of Comparative Examples 10 and 11 is too thick, the thermal stability is poor, and the puncture strength is also low, which makes it difficult to meet the use requirements of batteries.

[0112] In summary, by using the method provided by the embodiments of the present application, nano-porous alumina with good thermal stability, puncture resistance and liquid absorption capacity is prepared. The selection of raw materials (crystal grain inhibitors and pore-forming agents are indispensable) and process conditions (hydrothermal reaction conditions and calcination conditions) are both key reasons affecting the final performance of nano-porous alumina. They must be coordinated to obtain nano-porous alumina with target pore volume and crystal phase composition.

[0113] The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A nanoporous alumina, characterized by, The crystal form of the nanoporous alumina includes 30-100% theta phase and 0-70% delta phase by volume percentage; The nanoporous alumina has a fine pore volume of 0.05 to 0.15 cm3 / g in a pore diameter of 10 to 75 nm 3 / g.

2. The nanoporous alumina of claim 1, wherein, The nanoporous alumina has a pore volume of 0.1 to 0.3 cm 3 / g; The mass percentage of single crystal particles in the nanoporous alumina is greater than 90%, and the size of the single crystal particles is 30-100 nm; The crystal form of the nanoporous alumina includes 45-100% theta phase and 0-45% delta phase by volume percentage.

3. A method for producing a nanoporous alumina as claimed in claim 1 or 2, characterized in that, The nanoporous alumina precursor slurry is obtained by mixing an aluminum salt, a crystal grain inhibitor, a pore-forming agent, and water, and then performing a hydrothermal reaction.

4. The production method according to claim 3, characterized by, The mass of the crystal grain inhibitor is 0.005-0.2% of the mass of the aluminum salt, and the mass of the pore-forming agent is 0.01-2% of the mass of the aluminum salt; the mass ratio of the aluminum salt to water is 0.5:9.5-2:

8. Preferably, the crystal grain inhibitor includes at least one of sodium hydroxide, sodium polyacrylate, potassium hydroxide, and ammonia water. Preferably, the pore-forming agent includes triquaternary ammonium and / or trimethyl ammonium. Preferably, the aluminum salt includes at least one of aluminum hydroxide, pseudo-boehmite, and aluminum chloride. Preferably, the mixing of the aluminum salt, the crystal grain inhibitor, the pore-forming agent, and water is performed by sand milling for 1-5 hours.

5. The preparation method according to claim 3, characterized in that, The temperature of the hydrothermal reaction is 130-240°C, the reaction time is 6-50 hours, and the pressure in the reaction cavity is 1.5-3 MPa. Preferably, the temperature of the hydrothermal reaction is 170-220°C, and the reaction time is 9-30 hours.

6. The preparation method according to claim 3, characterized in that, The parameters of the calcination include a temperature rising rate of 1-10°C / min, a holding temperature of 600-1100°C, and a holding time of 0.5-10 hours; and the loading amount of the nanoporous alumina precursor powder is greater than or equal to 80% of the volume of the crucible. Preferably, the temperature rising rate of the calcination is 4-6°C / min, and the holding temperature is 800-1100°C.

7. The preparation method according to claim 3, characterized in that, The drying includes spray drying the nanoporous alumina precursor slurry after concentration. Preferably, the solid content of the nanoporous alumina precursor concentrate obtained by the concentration is greater than 30%. Preferably, the water content of the nanoporous alumina precursor powder obtained by the spray drying is less than or equal to 0.3%.

8. The preparation method according to claim 3, characterized in that, The nanoporous alumina slurry is obtained by sand milling the nanoporous alumina agglomerates obtained after the calcination. Preferably, the nanoporous alumina slurry obtained after the sand milling is further treated by ceramic membrane concentration and / or spray drying.

9. A lithium-ion battery separator, characterized by, The nanometer porous alumina coating layer coated on at least one side surface of the diaphragm body, and the raw material of the nanometer porous alumina coating layer includes the nanoporous alumina of claim 1 or 2 or the nanoporous alumina prepared by the method of any one of claims 3-8.

10. The nanoporous alumina of claim 1 or 2 or the nanoporous alumina prepared by the method of any one of claims 3-8 is applied in the field of batteries.

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