Preparation method of inorganic nanofiber composite diaphragm, diaphragm and lithium battery

Abstract

The invention discloses a preparation method of an inorganic nanofiber composite diaphragm, the diaphragm and a lithium battery, and the preparation method of the diaphragm comprises the following steps: dropwise adding a calcium chloride solution into a sodium oleate solution, stirring, cooling to room temperature, adding a sodium dihydrogen phosphate dihydrate solution, and stirring to prepare a first mixed solution; the first mixed solution is subjected to a high-pressure reaction, and hydroxyapatite nanowires are prepared; adding the sodium lignin sulfonate solution into the polyamide epichlorohydrin solution, and stirring to obtain a second mixed solution; bacterial cellulose and hydroxyapatite nanowires are dispersed in purified water, the second mixed solution is added and stirred, then vacuum filtration, drying and crosslinking are conducted, and the inorganic nanofiber composite diaphragm is prepared. The mechanical strength and tensile strength of the diaphragm are enhanced, and the thickness of the diaphragm is less than or equal to 16 microns.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a method for preparing an inorganic nanofiber diaphragm and a lithium battery. Background Art

[0002] In lithium-ion batteries, the diaphragm plays an irreplaceable role as a key inert component that separates the anode and cathode. However, most commercial diaphragms on the market are based on polyolefins, mainly polyethylene and polypropylene. This type of diaphragm has the following main problems: 1. The electrolyte affinity is poor, which limits the transmission efficiency of lithium ions in the diaphragm, thereby affecting the overall performance of the battery; 2. The ion conductivity is low and cannot meet the requirements for ion conduction speed during rapid charging and discharging, reducing the battery's charging and discharging efficiency; 3. Their inherent low thermal stability. During the use of the battery, once the temperature rises, the diaphragm is prone to shrinkage, deformation, or even melting, which brings great risks to the safe application of lithium-ion batteries and may cause serious accidents such as battery short circuits, fires, and even explosions.

[0003] To solve the above problems, the following methods are currently used: 1. Use inherent thermal safety materials to prepare diaphragms, such as aluminum oxide / polyvinylidene fluoride diaphragms and nanoporous polyimide membranes. Although these diaphragms have improved in thermal stability, they still have deficiencies in other properties. 2. Prepare non-flammable gel / solid electrolytes to enhance battery safety, but they face problems such as high costs and complex processes in practical applications. 3. Add heat-resistant inorganic ceramic coatings to commercial diaphragms (such as silica and halloysite) for surface modification, but this method has limited effect on improving the overall performance of the diaphragm.

[0004] Among the many improvement strategies, ceramic nanofiber separators have attracted much attention as an effective and feasible method. Compared with traditional inorganic nanoparticles or nanorods, inorganic ceramic fibers have extremely high thermal stability, flexibility and processability. For example, Jing et al. prepared pure zirconium dioxide nanowire separators by sol-assisted electrospinning. The separators showed good flexibility and electrochemical properties, but the tensile strength was only about 3.72MPa, which was far lower than the standard of about 10MPa required for commercial manufacturing, and it was difficult to meet the needs of large-scale industrial production. Obeidi et al. prepared a thin boehmite-polyvinylidene fluoride composite separator with a thickness of 22μm by coating, and the tensile strength was also low, only 6.30MPa. Li et al. synthesized hydroxyapatite nanowires with a high aspect ratio by hydrothermal method and combined them with cellulose fibers to prepare composite separators. Although the tensile strength reached 13.21MPa, the thickness of the separator (56μm) was about twice that of the commercial PP separator, which not only increased the overall weight and volume of the battery, but also may affect the energy density of the battery.

[0005] Therefore, it is urgent to develop a new diaphragm to solve the above problems. Summary of the invention

[0006] In order to overcome the defects in the prior art, the first purpose of the present invention is to provide a method for preparing an inorganic nanofiber composite membrane; the second purpose of the present invention is to provide an inorganic nanofiber composite membrane prepared by the above preparation method; the third purpose of the present invention is to provide a lithium battery having the above inorganic nanofiber composite membrane.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] In a first aspect, a method for preparing an inorganic nanofiber composite diaphragm comprises the following steps:

[0009] Adding the calcium chloride solution dropwise into the sodium oleate solution, stirring, cooling to room temperature, adding the sodium dihydrogen phosphate dihydrate solution and stirring to obtain a first mixed solution;

[0010] The first mixed solution is subjected to a high pressure reaction to prepare hydroxyapatite nanowires;

[0011] adding the sodium lignin sulfonate solution to the polyamide epichlorohydrin solution and stirring to obtain a second mixed solution;

[0012] The bacterial cellulose and hydroxyapatite nanowires are dispersed in pure water, a second mixed solution is added and stirred, and then vacuum filtration, drying and cross-linking are performed to obtain an inorganic nanofiber composite diaphragm.

[0013] In the preparation process of the inorganic nanofiber composite diaphragm, sodium lignin sulfonate, polyamide epichlorohydrin, bacterial cellulose and hydroxyapatite nanowires are mixed with each other, and the mechanical strength of the diaphragm is improved through the synergistic effect of chemical bonds, hydrogen bonds and electrostatic attraction. Specifically, the active groups in polyamide epichlorohydrin react chemically with the functional groups on sodium lignin sulfonate and bacterial cellulose to form covalent bonds. Through the connection method of chemical bonds, the various components are closely combined together, greatly enhancing the overall structural stability of the diaphragm. During the cross-linking process, a chemical reaction is triggered to form chemical bonds between the molecular chains of different components, connecting the originally relatively independent molecules into a huge network structure, so that the diaphragm can more effectively disperse stress when subjected to external forces, thereby improving the mechanical strength. Molecules such as sodium lignin sulfonate and bacterial cellulose contain a large number of polar groups such as hydroxyl groups (-OH). These polar groups interact with each other through hydrogen bonds. A large number of hydrogen bonds form an attraction between molecules, making the arrangement between molecules more compact and orderly, enhancing the mutual constraints between molecules, making the overall structure of the diaphragm more stable, and improving mechanical properties. Sodium lignin sulfonate is a high molecular compound with a negative charge, while hydroxyapatite nanowires and the like carry a positive charge under certain conditions. Electrostatic attraction occurs between positive and negative charges. This electrostatic attraction is like the attraction between the two poles of a magnet, which brings different components close to each other and tightly binds together. It helps to promote the uniform dispersion of various components in the solution, and further enhances the interaction between the components during the formation of the diaphragm, making the structure of the diaphragm more compact, thereby improving the mechanical strength of the diaphragm. The three forces of chemical bonds, hydrogen bonds and electrostatic attraction do not exist in isolation, but work in synergy. Chemical bonds provide a strong and stable connection and are the "skeleton" of the diaphragm structure; hydrogen bonds increase the interaction and order between molecules at the molecular level, making the structure more compact; electrostatic attraction promotes the uniform dispersion and mutual proximity of the components, and enhances the overall binding force. Together, they form a two-dimensional line-surface network structure between sodium lignin sulfonate, polyamide epichlorohydrin, bacterial cellulose and hydroxyapatite nanowires, effectively improving the mechanical strength of the diaphragm, so that it can better meet the requirements of lithium-ion batteries for diaphragm performance.

[0014] Preferably, before the calcium chloride solution is dripped into the sodium oleate solution, the method further comprises:

[0015] Dissolving sodium oleate in water at a preset temperature to obtain a sodium oleate solution; the preset temperature range is 70° C. to 100° C.;

[0016] Calcium chloride and sodium dihydrogen phosphate dihydrate are dissolved in water respectively to prepare calcium chloride solution and sodium dihydrogen phosphate dihydrate solution.

[0017] Further preferably, sodium oleate is dissolved in water at 80° C. to prepare a sodium oleate solution;

[0018] Preferably, the molar ratio of sodium oleate, calcium chloride and sodium dihydrogen phosphate dihydrate is (5-6): (1-2): 1, and the three are dissolved in the same volume of water. More preferably, the molar ratio of sodium oleate, calcium chloride and sodium dihydrogen phosphate dihydrate is 67:14:13.

[0019] Sodium oleate is dissolved at a preset temperature. The appropriate temperature can accelerate the dissolution rate of sodium oleate, so that it is fully dispersed in water to form a uniform solution, providing a good starting state for subsequent reactions. By precisely controlling the molar ratio of sodium oleate, calcium chloride, and sodium dihydrogen phosphate dihydrate, the crystallinity, aspect ratio and other structural parameters of the generated hydroxyapatite nanowires are guaranteed to be stable. If the raw material ratio is not appropriate, such as excessive sodium oleate, the chemical balance of the reaction will be destroyed, resulting in an irregular structure of the generated hydroxyapatite nanowires, which will in turn reduce the tensile strength and other properties of the diaphragm.

[0020] Preferably, the step of dripping calcium chloride solution into sodium oleate solution, stirring, cooling to room temperature, and then adding sodium dihydrogen phosphate dihydrate solution and stirring to obtain a first mixed solution comprises:

[0021] The calcium chloride solution is dripped into the sodium oleate solution, stirred for 0.5 to 1.5 hours, cooled to room temperature, and then sodium dihydrogen phosphate dihydrate solution is added and stirred for 0.5 to 1 hour to obtain a first mixed solution. Further preferably, the calcium chloride solution is dripped into the sodium oleate solution, stirred for 1 hour, cooled to room temperature, and then sodium dihydrogen phosphate dihydrate solution is added and stirred for 0.5 hour to obtain a first mixed solution.

[0022] The calcium chloride solution was dropped into the sodium oleate solution and stirred for 1 hour. Sufficient stirring time can make the calcium chloride and sodium oleate react fully, so that the calcium ions and the ions in the sodium oleate can be fully combined to form a uniform reaction intermediate product. After cooling to room temperature, sodium dihydrogen phosphate dihydrate solution was added and stirred for 0.5 hours. This is because high temperature may affect the reaction activity of sodium dihydrogen phosphate dihydrate and the stability of the product. Stirring at room temperature can make it react smoothly with the previous reaction product to generate a more stable first mixed solution, laying the foundation for the subsequent generation of high-quality hydroxyapatite nanowires.

[0023] Preferably, the step of subjecting the first mixed solution to a high pressure reaction to prepare hydroxyapatite nanowires comprises:

[0024] transferring the first mixed solution to a stainless steel autoclave lined with polytetrafluoroethylene for high pressure reaction to obtain monodispersed hydroxyapatite nanowires;

[0025] The monodispersed hydroxyapatite nanowires are washed and the self-assembled hydroxyapatite nanowires are collected.

[0026] Preferably, the reaction temperature of the high pressure reaction is 150-250°C, and the reaction time is 30-40 hours. Further preferably, the reaction temperature of the high pressure reaction is 200°C, and the reaction time is 36 hours.

[0027] Further preferably, the monodispersed hydroxyapatite nanowires are washed alternately with ultrapure water and ethanol at least three times to collect the self-assembled hydroxyapatite nanowires.

[0028] The first mixed solution is transferred to a stainless steel autoclave lined with polytetrafluoroethylene. The polytetrafluoroethylene lining can prevent the solution from chemically reacting with the metal wall of the autoclave, thereby ensuring a pure reaction environment.

[0029] The high-pressure reaction conditions of 200°C and 36h were obtained through experimental optimization. Under these conditions, the thermal motion of molecules is intensified, which can promote the chemical reaction in the direction of generating hydroxyapatite nanowires and form a monodispersed nanowire structure. In addition, suitable high-pressure reaction conditions can produce hydroxyapatite nanowires with good crystallinity and suitable aspect ratio. Such nanowires have high thermal stability and mechanical strength, providing excellent thermal stability and enhanced mechanical properties for the diaphragm. Wash alternately with ultrapure water and ethanol at least three times. Ultrapure water can wash away water-soluble impurities on the surface of the nanowires, and ethanol can remove some organic impurities and help dry, so as to prevent impurities from affecting the electrolyte wettability of the diaphragm. If impurities remain, the diaphragm will not be able to effectively infiltrate the electrolyte in the lithium battery, reducing the battery performance.

[0030] Preferably, the step of adding the sodium lignin sulfonate solution to the polyamide epichlorohydrin solution and stirring to obtain the second mixed solution comprises:

[0031] preparing a sodium lignin sulfonate solution and a polyamide epichlorohydrin solution each having a weight percentage of 1 to 5%;

[0032] The prepared sodium lignin sulfonate solution and the polyamide epichlorohydrin solution are mixed and stirred for 20 to 40 minutes to obtain a sodium lignin sulfonate-polyamide epichlorohydrin mixed solution (a second mixed solution).

[0033] Weight percentage is a way to express the content of a component in a mixture. It refers to the ratio of the mass of the component to the total mass of the mixture, multiplied by 100%, to reflect the mass proportion of the component in the entire mixture. For example, a sodium lignin sulfonate solution with a weight percentage of 1% means that in the solution, the mass of sodium lignin sulfonate accounts for 1% of the total mass of the solution; similarly, a polyamide epichlorohydrin solution with a weight percentage of 1% means that the mass of polyamide epichlorohydrin accounts for 1% of the total mass of the solution. Among them, the preparation of sodium lignin sulfonate solution and polyamide epichlorohydrin solution is a conventional step. That is, sodium lignin sulfonate or polyamide epichlorohydrin is dissolved in water according to a preset ratio to form a uniform solution.

[0034] Further preferably, a sodium lignin sulfonate solution and a polyamide epichlorohydrin solution are prepared with a weight percentage of 1% each;

[0035] The prepared sodium lignin sulfonate solution with a weight percentage of 1% and the polyamide epichlorohydrin solution were mixed and stirred for 30 minutes to prepare a sodium lignin sulfonate-polyamide epichlorohydrin mixed solution with a weight percentage of 1% (second mixed solution).

[0036] A uniform mixed solution formed by appropriate concentration and sufficient stirring can effectively enhance the internal bonding force of the diaphragm. In the diaphragm, this mixed solution acts as a reinforcing agent and synergizes with other ingredients to improve the mechanical properties of the diaphragm, such as tensile strength. If the concentration is not appropriate or the stirring is not sufficient, the mixed solution will be uneven, forming weak areas in the diaphragm and reducing the overall performance of the diaphragm.

[0037] Preferably, the method of dispersing bacterial cellulose and hydroxyapatite nanowires in pure water, adding the second mixed solution and stirring, and then vacuum filtering, drying, and cross-linking to obtain an inorganic nanofiber composite membrane comprises:

[0038] Dispersing bacterial cellulose and hydroxyapatite nanowires in a mass ratio of 1:(5-6) in pure water to obtain a third mixed solution;

[0039] Adding the second mixed solution to the third mixed solution and stirring for 20 to 40 minutes to obtain a fourth mixed solution;

[0040] The fourth mixed solution is vacuum filtered, dried, and cross-linked to obtain an inorganic nanofiber composite diaphragm.

[0041] Bacterial cellulose and hydroxyapatite nanowires are dispersed in a mass ratio of 1:(5-6). At this ratio, bacterial cellulose and hydroxyapatite nanowires can form an interwoven stable structure in the membrane, giving full play to their respective advantages, so that the membrane has good flexibility and mechanical strength.

[0042] Further preferably, the mass of the pure water is ≥ five times the total mass of the bacterial cellulose and the hydroxyapatite nanowires. Sufficient pure water can fully disperse the two materials to form a uniform dispersion system and avoid agglomeration that affects performance.

[0043] More preferably, the cross-linking temperature is 90-110° C. and the cross-linking time is 0.9-1.2 h. Such cross-linking conditions can form stable chemical bonds between molecules, further enhancing the structural stability of the diaphragm.

[0044] In a second aspect, an inorganic nanofiber composite membrane is provided, wherein the inorganic nanofiber composite membrane is prepared by the above-mentioned method for preparing the inorganic nanofiber composite membrane.

[0045] Preferably, the diaphragm has a thickness of ≤16 μm, a tensile strength of ≥16.6 MPa, and a Young's modulus of 3.99 GPa.

[0046] Young's modulus, also known as tensile modulus, is a physical quantity that describes the ability of a solid material to resist deformation. It measures the amount of stress required for a material to undergo unit strain within its elastic limit. Simply put, the larger the Young's modulus, the less likely the material is to deform when subjected to force, that is, the "harder" the material is; conversely, the smaller the Young's modulus, the easier the material is to deform. In the present invention, the Young's modulus of the inorganic nanofiber composite diaphragm is 3.99 GPa, and the diaphragm has good mechanical properties, which helps to ensure the structural stability of the lithium battery during use.

[0047] In a third aspect, a lithium battery comprises a positive electrode, a negative electrode, an electrolyte and a separator disposed between the positive electrode and the negative electrode, wherein the separator is the above-mentioned inorganic nanofiber composite separator.

[0048] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0049] 1. Sodium lignin sulfonate, polyamide epichlorohydrin, bacterial cellulose and hydroxyapatite nanowires work synergistically through chemical bonds, hydrogen bonds and electrostatic attraction to form a complex and stable network structure, which improves the mechanical strength of the diaphragm. The tensile strength is ≥16.6MPa and the Young's modulus is 3.99GPa.

[0050] 2. The thickness of the diaphragm is ≤16μm, which may be beneficial to the internal ion conduction and other performance of the battery while ensuring the mechanical strength.

[0051] 3. As a lithium battery separator, it can better meet the requirements of lithium-ion batteries for separator performance with its excellent mechanical properties and appropriate thickness, and help improve the overall performance of lithium batteries.

[0052] In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0054] Figure 1 It is the diaphragm spectrum in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0055] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] Embodiment 1:

[0057] A method for preparing an inorganic nanofiber composite diaphragm comprises the following steps:

[0058] A sodium oleate solution was prepared by dissolving 2.06 g of sodium oleate in 25 g of water at 80°C.

[0059] 0.15 g of calcium chloride and 0.197 g of sodium dihydrogen phosphate dihydrate were decomposed and dissolved in 25 g of water to prepare a calcium chloride solution and a sodium dihydrogen phosphate dihydrate solution.

[0060] The calcium chloride solution was slowly dripped into the sodium oleate solution and stirred for 1 hour. After cooling to room temperature, sodium dihydrogen phosphate dihydrate solution was added and stirred for 0.5 hours to obtain a first mixed solution.

[0061] The first mixed solution was transferred to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave and maintained at 200° C. for 36 h to obtain monodispersed hydroxyapatite nanowires. The monodispersed hydroxyapatite nanowires were washed alternately with ultrapure water and ethanol three times to collect the self-assembled hydroxyapatite nanowires.

[0062] A sodium lignin sulfonate solution and a polyamide epichlorohydrin solution with a weight percentage of 1% were prepared respectively. The prepared sodium lignin sulfonate solution with a weight percentage of 1% was slowly added to the polyamide epichlorohydrin solution with a weight percentage of 1%, and stirred at a rotation speed of 300 rpm for 30 minutes to obtain a 1 weight% sodium lignin sulfonate-polyamide epichlorohydrin mixed solution.

[0063] 3.15 mg of bacterial cellulose and 17.85 mg of hydroxyapatite nanowires were dispersed in 150 ml of pure water at high speed for 4 min, and then a sodium lignin sulfonate-polyamide epichlorohydrin mixed solution was added and stirred for 30 min to combine. Subsequently, the product was filtered and dried under vacuum, and cross-linked at 100 ° C for 1 h to obtain an inorganic nanofiber composite membrane.

[0064] This embodiment also provides an inorganic nanofiber composite diaphragm prepared by the above-mentioned method for preparing an inorganic nanofiber composite diaphragm. The diaphragm has a thickness of ≤16 μm, a tensile strength of ≥16.28 MPa, and a Young's modulus of 3.99 GPa.

[0065] This embodiment also provides a lithium battery assembled using the inorganic nanofiber composite diaphragm. The lithium battery comprises a positive electrode, a negative electrode, an electrolyte, and an inorganic nanofiber composite diaphragm disposed between the positive electrode and the negative electrode.

[0066] Comparative Example 1:

[0067] A method for preparing a diaphragm comprises the following steps:

[0068] 8 g of sodium oleate was dissolved in 25 g of water at 80°C to prepare a sodium oleate solution.

[0069] 0.15 g of calcium chloride and 0.197 g of sodium dihydrogen phosphate dihydrate were decomposed and dissolved in 25 g of water to prepare a calcium chloride solution and a sodium dihydrogen phosphate dihydrate solution.

[0070] The calcium chloride solution was slowly dripped into the sodium oleate solution and stirred for 1 hour. After cooling to room temperature, sodium dihydrogen phosphate dihydrate solution was added and stirred for 0.5 hours to obtain a first mixed solution.

[0071] The first mixed solution was transferred to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave and maintained at 200° C. for 36 h to obtain monodispersed hydroxyapatite nanowires. The monodispersed hydroxyapatite nanowires were washed alternately with ultrapure water and ethanol three times to collect the self-assembled hydroxyapatite nanowires.

[0072] A sodium lignin sulfonate solution and a polyamide epichlorohydrin solution with a weight percentage of 1% were prepared respectively. The prepared sodium lignin sulfonate solution with a weight percentage of 1% was slowly added to the polyamide epichlorohydrin solution with a weight percentage of 1%, and stirred at a rotation speed of 300 rpm for 30 minutes to obtain a 1 weight% sodium lignin sulfonate-polyamide epichlorohydrin mixed solution.

[0073] 3.15 mg of bacterial cellulose and 17.85 mg of hydroxyapatite nanowires were dispersed in 150 ml of pure water at high speed for 4 min, and then a sodium lignin sulfonate-polyamide epichlorohydrin mixed solution was added and stirred for 30 min to combine. Subsequently, the product was filtered and dried under vacuum, and cross-linked at 100 ° C for 1 h to obtain an inorganic nanofiber composite membrane.

[0074] This comparative example 1 also provides a diaphragm prepared using the above diaphragm preparation method.

[0075] This comparative example 1 also provides a lithium battery assembled using the above-mentioned separator. The lithium battery comprises a positive electrode, a negative electrode, an electrolyte and a separator disposed between the positive electrode and the negative electrode.

[0076] Comparative Example 2:

[0077] A method for preparing a diaphragm comprises the following steps:

[0078] A sodium oleate solution was prepared by dissolving 2.06 g of sodium oleate in 25 g of water at 80°C.

[0079] 0.15 g of calcium chloride and 0.197 g of sodium dihydrogen phosphate dihydrate were decomposed and dissolved in 25 g of water to prepare a calcium chloride solution and a sodium dihydrogen phosphate dihydrate solution.

[0080] The calcium chloride solution was slowly dripped into the sodium oleate solution and stirred for 1 hour. After cooling to room temperature, sodium dihydrogen phosphate dihydrate solution was added and stirred for 0.5 hours to obtain a first mixed solution.

[0081] The first mixed solution was transferred to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave and maintained at 200° C. for 36 h to obtain monodispersed hydroxyapatite nanowires. The monodispersed hydroxyapatite nanowires were washed alternately with ultrapure water and ethanol three times to collect the self-assembled hydroxyapatite nanowires.

[0082] A sodium lignin sulfonate solution and a polyamide epichlorohydrin solution with a weight percentage of 1% were prepared respectively. The prepared sodium lignin sulfonate solution with a weight percentage of 1% was slowly added to the polyamide epichlorohydrin solution with a weight percentage of 1%, and stirred at a rotation speed of 300 rpm for 30 minutes to obtain a 1 weight% sodium lignin sulfonate-polyamide epichlorohydrin mixed solution.

[0083] 17.85 mg of bacterial cellulose and 3.15 mg of hydroxyapatite nanowires were dispersed in 150 ml of pure water at high speed for 4 min, and then a sodium lignin sulfonate-polyamide epichlorohydrin mixed solution was added and stirred for 30 min to combine. Subsequently, the product was filtered and dried under vacuum, and cross-linked at 100 ° C for 1 h to obtain an inorganic nanofiber composite membrane.

[0084] This comparative example 1 also provides a diaphragm prepared using the above diaphragm preparation method.

[0085] This comparative example 1 also provides a lithium battery assembled using the above-mentioned separator. The lithium battery comprises a positive electrode, a negative electrode, an electrolyte and a separator disposed between the positive electrode and the negative electrode.

[0086] The following tests were performed on the diaphragms and lithium batteries prepared in the above Example 1 and Comparative Examples 1 and 2, and the lithium battery prepared by the PP diaphragm as Comparative Example 3:

[0087] 1. The crystal structure and functional group type of the membrane were characterized by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy, respectively. X-ray photoelectron spectroscopy (XPS) analysis was performed to analyze the elemental composition and content.

[0088] 2. Use a universal tensile testing machine (C41.103, S insans e) to test the tensile strength of the diaphragm.

[0089] 3. Measure the contact angle of the diaphragm using a contact angle meter (XG-CAMB3).

[0090] 4. The thermal behavior of the membrane was characterized by thermogravimetric analysis and differential scanning calorimetry (TG-DSC, STA449F3, Net zs ch).

[0091] Battery formula: positive electrode (16.0 mg / cm on each side 2 ) is composed of NCM811, Super P, PVDF 5130 and CNT in a weight ratio of 96:1.8:1.7:0.5. Negative electrode (10.1 mg / cm on each side 2 ) is composed of graphite, LA136D, Super P, CNT and CMC in a weight ratio of 96:2.3:0.9:0.4:0.4. The N / P value is close to 1.13. The electrolyte contains 1M L iPF6 / EC:EMC (volume ratio is 3:7). The diaphragm is the corresponding diaphragm prepared in the examples and comparative examples. All batteries use copper foil with a thickness of 6.0μm as the negative electrode current collector. The charge and discharge range is 2.0-4.5V.

[0092]

[0093] See also Figure 1 The XRD spectrum shows that Example 1 perfectly realizes the self-assembly of bacterial cellulose, sodium lignin sulfonate, and hydroxyapatite nanowires, while in Comparative Example 2, due to the excessive ratio, the self-assembly cannot occur in an orderly manner, destroying the structure of sodium lignin sulfonate or hydroxyapatite nanowires.

[0094] The tensile strength test shows that the composite membrane in Example 1 has a super tensile strength of 16.6 MPa, which is much higher than that of the PP membrane. At the same time, the structural failure of sodium lignin sulfonate or hydroxyapatite nanowires will reduce the tensile strength of the composite membrane.

[0095] The contact angle experiment shows that Example 1 has the smallest contact angle, and has excellent wetting performance and liquid retention ability.

[0096] The PP separator showed obvious bending at 120°C and shrunk severely as the temperature increased. When the temperature rose to 200°C, the PP separator completely shrunk and lost the ability to isolate the electrodes, resulting in thermal runaway. In contrast, the composite separator did not shrink even when the temperature exceeded 200°C, which shows the reliability of the inorganic nanofiber composite separator prepared by the present invention in preventing battery short circuits under high temperature conditions.

[0097] The electrochemical performance test shows that the capacity retention rate of NCM811 / Gr 200 cycles with the composite membrane in Example 1 is 97%, and the long cycle performance is excellent.

[0098] The present invention uses specific embodiments to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A method for preparing an inorganic nanofiber composite diaphragm, characterized in that: The following steps are involved: Adding the calcium chloride solution dropwise into the sodium oleate solution, stirring, cooling to room temperature, adding the sodium dihydrogen phosphate dihydrate solution and stirring to obtain a first mixed solution; The first mixed solution is subjected to a high pressure reaction to prepare hydroxyapatite nanowires; adding the sodium lignin sulfonate solution to the polyamide epichlorohydrin solution and stirring to obtain a second mixed solution; The bacterial cellulose and hydroxyapatite nanowires are dispersed in pure water, a second mixed solution is added and stirred, and then vacuum filtration, drying and cross-linking are performed to obtain an inorganic nanofiber composite diaphragm.

2. The method for preparing the inorganic nanofiber composite diaphragm according to claim 1, characterized in that: Before dropping the calcium chloride solution into the sodium oleate solution, the method also includes: Dissolve sodium oleate in water at 70°C to 100°C to prepare a sodium oleate solution; Dissolving calcium chloride and sodium dihydrogen phosphate dihydrate in water respectively to prepare a calcium chloride solution and a sodium dihydrogen phosphate dihydrate solution; Preferably, sodium oleate is dissolved in water at 80° C. to prepare a sodium oleate solution; Preferably, the molar ratio of sodium oleate, calcium chloride and sodium dihydrogen phosphate dihydrate is (5-6):(1-2):1, and the three are dissolved in the same volume of water respectively.

3. The method for preparing an inorganic nanofiber separator according to claim 1: the step of dripping a calcium chloride solution into a sodium oleate solution, stirring, cooling to room temperature, and then adding a dihydrate sodium dihydrogen phosphate solution and stirring to obtain a first mixed solution comprises: The calcium chloride solution was dropped into the sodium oleate solution, stirred for 0.5 to 1.5 hours, cooled to room temperature, and then sodium dihydrogen phosphate dihydrate solution was added and stirred for 0.5 to 1 hour to prepare a first mixed solution.

4. The method for preparing the inorganic nanofiber membrane according to claim 1, characterized in that: The step of subjecting the first mixed solution to a high pressure reaction to prepare hydroxyapatite nanowires comprises: transferring the first mixed solution to a stainless steel autoclave lined with polytetrafluoroethylene for high pressure reaction to obtain monodispersed hydroxyapatite nanowires; washing the monodispersed hydroxyapatite nanowires and collecting the self-assembled hydroxyapatite nanowires; Preferably, the reaction temperature of the high pressure reaction is 150-250°C, and the reaction time is 30-40h; Preferably, the monodispersed hydroxyapatite nanowires are washed alternately with ultrapure water and ethanol at least three times to collect the self-assembled hydroxyapatite nanowires.

5. The method for preparing an inorganic nanofiber composite diaphragm according to claim 1, wherein the sodium lignin sulfonate solution is added to the polyamide epichlorohydrin solution and stirred to obtain a second mixed solution, comprising: preparing a sodium lignin sulfonate solution and a polyamide epichlorohydrin solution each having a weight percentage of 1 to 5%; The prepared sodium lignin sulfonate solution and the polyamide epichlorohydrin solution are mixed and stirred for 20 to 40 minutes to obtain a sodium lignin sulfonate-polyamide epichlorohydrin mixed solution.

6. The method for preparing the inorganic nanofiber membrane according to claim 1, characterized in that: The method comprises dispersing bacterial cellulose and hydroxyapatite nanowires in pure water, adding a second mixed solution and stirring, and then vacuum filtering, drying, and cross-linking to obtain an inorganic nanofiber composite membrane, comprising: Dispersing bacterial cellulose and hydroxyapatite nanowires in a mass ratio of 1:(5-6) in pure water to obtain a third mixed solution; Adding the second mixed solution to the third mixed solution and stirring for 20 to 40 minutes to obtain a fourth mixed solution; vacuum filtering, drying, and cross-linking the fourth mixed solution to obtain an inorganic nanofiber composite membrane; Preferably, the mass of the pure water is ≥ five times the total mass of the bacterial cellulose and the hydroxyapatite nanowires; Preferably, the cross-linking temperature is 90-110° C., and the cross-linking time is 0.9-1.2 h.

7. An inorganic nanofiber composite membrane, characterized in that: The inorganic nanofiber composite diaphragm is prepared by the method for preparing the inorganic nanofiber composite diaphragm according to any one of claims 1 to 6.

8. The inorganic nanofiber composite diaphragm according to claim 7, characterized in that: The diaphragm has a thickness of ≤16 μm, a tensile strength of ≥16.28 MPa, and a Young's modulus of 3.99 GPa.

9. A lithium battery, characterized in that: The invention comprises a positive electrode, a negative electrode, an electrolyte and a separator arranged between the positive electrode and the negative electrode, wherein the separator is the inorganic nanofiber composite separator according to any one of claims 7 to 8.

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