Fiber separator for lithium battery and method for manufacturing the same

Abstract

The application relates to a fiber diaphragm for a lithium battery and a preparation method thereof, and the fiber diaphragm for the lithium battery is an electrostatic spinning PI / oPAN nanofiber membrane; the PI / oPAN nanofiber membrane is composed of PI fibers and oPAN fibers which are arranged in an interlaced and stacked mode, the diameter of the PI fibers is 0.45-0.55 mu m, and the diameter of the oPAN fibers is 0.14-0.26 mu m; the preparation method of the fiber diaphragm for the lithium battery is as follows: firstly, polyamide acid and polyacrylonitrile are cross spun to obtain a PAA / PAN nanofiber membrane; then, the PAA / PAN nanofiber membrane is subjected to roll pressing treatment; and finally, the PAA / PAN nanofiber membrane after the roll pressing treatment is subjected to heating treatment to obtain a PI / oPAN nanofiber membrane. The method is simple in process, only needs to add one same spinning device, and does not need to add other substances or equipment; PAA and PAN monomers are separately configured into solutions, the optimal concentration for spinning can be achieved, and there is no mutual interference between the components before spinning; the fiber diaphragm for the lithium battery prepared by the method has a significantly improved mechanical property, and the ionic conductivity is better than that of the prior art.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery separators, and relates to a fiber separator for lithium batteries and a preparation method thereof. BACKGROUND

[0002] As a component of lithium ion batteries, the separator does not participate in electrochemical reactions, but plays an important role in isolating the positive and negative electrodes and transmitting lithium ions. Currently used commercial polyolefin separators such as PP and PE have the advantages of good mechanical strength and low cost, but the low electrolyte absorption, the non-uniform pores caused by the dry / wet preparation process, and the low porosity limit their development. Electrospinning can prepare nanofiber membranes with high porosity and uniform pores, but the mechanical strength is limited due to the disordered stacking of fibers. Polyimide (PI) is a high-performance material with high thermal stability, flame retardance, and high strength. PI nanofiber membranes prepared by electrospinning technology have been applied in the field of lithium battery separators. Polyacrylonitrile (PAN) has an electrolyte-polar group, and the study of electrospun PAN nanofiber separators has also been reported.

[0003] Generally, PI nanofiber membranes are prepared by mixing monomers of pyromellitic dianhydride (PMDA) and oxydianiline (ODA) in a solution, electrospinning to prepare a precursor polyamide acid (PAA) fiber membrane, and then heat-imidizing the fiber membrane at a high temperature of 300℃ to form a PI nanofiber membrane. PAN is a common carbon fiber raw material, which needs to be pre-oxidized at about 300℃ in the process of preparing carbon fibers to make the linear molecular chain of PAN cyclize, dehydrogenate and oxidize. The semi-carbon PAN fiber after pre-oxidation treatment retains some physical properties of PAN. Moreover, PAN will melt at a heat treatment temperature of 300℃, which can bond fibers and enhance the mechanical strength of the fiber membrane. Therefore, by compounding PAA and PAN and simultaneously performing heat treatment to complete imidization and pre-oxidation, the prepared composite fiber can have the characteristics of both PI and PAN, and has good thermal performance.

[0004] In the prior art, most of the PAA and PAN are mixed after being dissolved in solution (Study on preparation of polyacrylonitrile / polyimide composite lithium-ion battery separator by electrospinning, Journal of Materials Research, 2019, 34, 642-651; patent CN202111042970.4), and then the mixed solution is prepared into nanocomposite fibers by electrospinning, and the fibers are treated at high temperature. However, the solution mixing method for preparing composite fibers has the following problems: (1) the concentration of the spinning solution is limited by the mixing of the two components, and the best concentration of the single component fiber cannot be achieved; (2) the same voltage is used for PAN and PI through the same spinneret, and the best voltage and collection distance for each spinning cannot be selected; (3) the compatibility problem exists in the same fiber containing two components, which will produce more weak joints, thereby reducing the overall mechanical properties of the separator. A work (A nano-silica / polyacrylonitrile / polyimide composite separator for advanced fast charging lithium-ion batteries, Chemical Engineering Journal, 2021, 417:128075) adds inorganic particles in the solution during the preparation of PI / PAN composite fibers in the solution mixing method, which can improve the mechanical strength, but the addition of particles will increase the cost of the separator, and the uniformity of the particle distribution cannot be fully guaranteed. Patent CN202111042970.4 uses a coaxial electrospinning method to prepare a PAN@PAA composite membrane with PAA as the core and PAN as the shell, and then adds titanium dioxide by immersion method and performs thermal imidization to obtain a composite membrane. Although coaxial electrospinning can achieve the best concentration of components, the voltage and collection distance are fixed, and the best morphology of the fiber cannot be prepared. In addition, the coaxial process and the addition of metal particles increase the cost and process complexity. At the same time, this work separates the PAA and PAN solutions, which improves the mechanical strength and electrochemical performance of the membrane, but direct heat treatment will cause the shell to adhere to a large extent, which limits the improvement of the mechanical strength (maximum of 10.2 MPa) and ionic conductivity (maximum of 1.87 mS / cm).

[0005] Therefore, it is of great practical significance to develop a simple process that can combine PAN pre-oxidation and PAA thermal imidization, and maximize the performance advantages of the two components to prepare a battery separator with high mechanical properties, thermal dimensional stability, and excellent electrochemical performance. SUMMARY

[0006] The present application aims to solve the above problems in the prior art, and provides a fiber separator for lithium batteries and a preparation method thereof.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0008] A fiber separator for lithium batteries, which is an electrostatic spinning PI / oPAN nanofiber membrane;

[0009] The PI / oPAN nanofiber membrane is composed of PI (polyimide) fibers and oPAN (pre-oxidized polyacrylonitrile) fibers arranged in an interlaced and stacked manner, the average diameter of the PI fibers is 0.45-0.55 μm, and the average diameter of the oPAN fibers is 0.14-0.26 μm.

[0010] The oPAN fibers and the PI fibers of the present application are uniformly interlaced in the separator, the high porosity, micron-level pore size and nanometer-level fibers of the fiber membrane help to improve the ionic conductivity, and the uniformly interlaced fibers can reduce the effect of weak joints of the separator and improve the mechanical properties of the separator.

[0011] As a preferred technical scheme:

[0012] The fiber separator for lithium batteries has an average pore size of 0.8-1.2 μm and a porosity of 64.8-73.4%.

[0013] The fiber separator for lithium batteries has a tensile strength of 22.4-35.3 MPa and an ionic conductivity of 1.78-4.65 mS / cm.

[0014] The present application also provides a preparation method of the fiber separator for lithium batteries as described above, which comprises the following steps: firstly, cross spinning polyamide acid (PAA) spinning solution and polyacrylonitrile (PAN) spinning solution to obtain a PAA / PAN nanofiber membrane; secondly, roll pressing the PAA / PAN nanofiber membrane; and finally, heating the roll-pressed PAA / PAN nanofiber membrane to obtain a PI / oPAN nanofiber membrane, i.e., the fiber separator for lithium batteries;

[0015] The cross spinning of the polyamide acid spinning solution and the polyacrylonitrile spinning solution to obtain a PAA / PAN nanofiber membrane refers to using two independent electrostatic spinning devices to electrostatically spin the polyamide acid spinning solution and the polyacrylonitrile spinning solution, respectively, and using the same collection roller to collect the PAA / PAN nanofiber membrane.

[0016] Compared with the solution mixing spinning and then heating treatment, the PAA component and the PAN component will be in the same fiber after the solution mixing spinning, and the shrinkage degree of the PAA component and the PAN component in the heating process is not the same, which will cause the inconsistent shrinkage of each fiber, and finally the uneven thickness and the reduced mechanical properties. In the present application, the cross spinning is followed by the heat treatment, and the single fiber is pure PAA or pure PAN, and finally the PI fiber and the pre-oxidized PAN fiber are formed in the uniform thickness and are stacked alternately, which can improve the mechanical strength.

[0017] The heating treatment after the cross spinning in the present application has the consistency based on the thermal imidization of the PI fiber and the pre-oxidation of the PAN fiber, and one step simultaneously completes the imidization of the PAA and the pre-oxidation of the PAN, which improves the resource utilization rate, meets the clean and energy-saving direction of the modern battery industry, and improves the mechanical strength and the ion conductivity of the membrane.

[0018] As a preferred technical solution:

[0019] The preparation method of the fiber separator for the lithium battery as described above has the following specific steps:

[0020] (1) diamino diphenyl ether (ODA) is added to DMAc, and stirred at room temperature until completely dissolved to obtain a diamino diphenyl ether solution, and then pyromellitic dianhydride (PMDA) is added to the diamino diphenyl ether solution in batches (too much PMDA is added at one time, which will cause the powder to form a group and is not conducive to dissolution), and stirred to form a polyamide acid spinning solution;

[0021] (2) polyacrylonitrile is added to DMAc, and stirred at room temperature until completely dissolved to obtain a polyacrylonitrile spinning solution;

[0022] (3) the polyamide acid spinning solution obtained in step (1) and the polyacrylonitrile spinning solution obtained in step (2) are electrospun respectively, and the same collection roller is used for collection to obtain a PAA / PAN nanofiber membrane;

[0023] (4) the PAA / PAN nanofiber membrane obtained in step (3) is subjected to roller pressing treatment, and the density is 0.6±0.05 g / cm 3 ;

[0024] (5) the PAA / PAN nanofiber membrane after the roller pressing treatment in step (4) is fixed on an aluminum foil, and is heated in a muffle furnace at a temperature rising speed of 10±5 ℃ / min from room temperature to 250-350 ℃ and kept for 2 h to obtain a PI / oPAN nanofiber membrane, i.e. a fiber separator for a lithium battery; the imidization degree of PAA is reduced if the heat treatment time is too short, and the PAN fiber is broken if the heat treatment time is too long Figure 4 and Figure 5), the degree of imidization of PAA is reduced when the heat treatment temperature is low, and the fiber morphology of PAN is lost when the heat treatment temperature is too high Figure 5 and Figure 6 Therefore, the present application selects a heat treatment temperature and time with the best comprehensive performance.

[0025] The preparation method of the fiber separator for lithium battery as described above, in step (1), the pyromellitic dianhydride is gradually added to the solution of p-phenylenediamine in a mass ratio of 6:3:1.

[0026] The preparation method of the fiber separator for lithium battery as described above, in step (1), the mass fraction of pyromellitic dianhydride in the polyamide acid spinning solution is 12-14wt%, and the mass fraction of p-phenylenediamine is 11-13wt%.

[0027] The preparation method of the fiber separator for lithium battery as described above, in step (2), the concentration of the polyacrylonitrile spinning solution is 10-12wt%.

[0028] The preparation method of the fiber separator for lithium battery as described above, in step (3), the volume ratio of the polyamide acid spinning solution to the polyacrylonitrile spinning solution is 0.9-1.2:0.9-1.

[0029] The preparation method of the fiber separator for lithium battery as described above, in step (3), the process parameters of electrospinning are as follows:

[0030] For polyamide acid, the spinning voltage is 18-20kV, the distance between the spinning head and the collecting roller is 16-18cm, and the advancing speed is 0.8-1mL / h;

[0031] For polyacrylonitrile, the spinning voltage is 15-17kV, the distance between the spinning head and the collecting roller is 13-15cm, and the advancing speed is 0.8-1mL / h.

[0032] The principle of the present application is as follows:

[0033] The present application adopts the method of cross spinning to prepare PAA / PAN nanofiber membrane, and then performs heat treatment to obtain PI / oPAN nanofiber membrane, which has good mechanical strength and ionic conductivity.

[0034] On the one hand, the PI / oPAN nanofiber membrane prepared by cross spinning and heating has high mechanical strength:

[0035] (1) Compared with the PAA / PAN nanofiber membrane prepared by solution mixing and then electrospinning, in the application, the PAA spinning solution and the PAN spinning solution are separated, the PAA spinning solution and the PAN spinning solution can reach the most suitable concentration for fiber formation respectively, the voltage, the collection distance and other parameters can reach the optimum during spinning, and the PAA and the PAN are not coexistent in the same fiber after spinning, but form fibers alone, that is, the fiber formed after spinning has excellent performance;

[0036] (2) Compared with the fiber membrane heated after solution mixing and spinning, in the application, the PAA fibers will shrink alone to form PI fibers when the fiber membrane is heated, and the PAN fibers will also shrink alone to form oPAN fibers, which can avoid the uneven thickness of each fiber caused by different shrinkage of the two components in the fiber during heating after solution mixing and spinning, that is, the heat treatment of the application will not increase the uneven thickness of the fiber;

[0037] (3) The PAN fibers will produce adhesion during heat treatment, compared with heating after solution mixing and spinning, in the application, due to the independence of the PAN fibers and the PI fibers in the fiber membrane, the heat treatment will not cause adhesion of each fiber, avoiding the shortcomings of decreased porosity and mechanical properties caused by excessive adhesion;

[0038] (4) PAA completely heat imidization to PI requires a temperature of about 300 DEG C, and the mechanical strength of PAN will be greatly reduced when the heat treatment exceeds 300 DEG C. In order to ensure the complete heat imidization of PAA, the application adopts heat treatment at about 300 DEG C, but since the PAA and the PAN fibers exist separately in the composite membrane, although the performance of the PAN fibers in the membrane will decrease during heat treatment, the mechanical strength of the PAA imidization to PI in the membrane is continuously improved, and the separate existence of the PI fibers ensures the integrity of the main body of the composite membrane and the mechanical properties. The composite fibers prepared by the solution mixing and spinning method in the prior art will have the mechanical strength of the PAA component improved during heat treatment, but since the PAN component is contained in all the fibers, the fiber strength will be reduced by high temperature heating, and the two opposite effects will limit the improvement of the mechanical properties of each fiber, and further limit the improvement of the mechanical properties of the whole fiber membrane.

[0039] On the other hand, the PI / oPAN nanofiber membrane prepared by cross spinning and then heating in the application has high ionic conductivity:

[0040] (1) Cross spinning can make PAA fibers and PAN fibers uniformly composite, and electrospinning technology gives the separator good porosity and uniform pore size; (2) PI fiber membrane itself has high ionic conductivity; (3) The degree of graphitization of PAN after pre-oxidation is improved, and the ionic conductivity of graphite is very high, the deeper the degree of graphitization, the greater the ionic conductivity, so pre-oxidized PAN (i.e. oPAN) also improves the ionic conductivity; (4) The shrinkage of PAA fibers and PAN fibers during heating increases the voids in the membrane, and improving the porosity can give lithium ion transmission a larger channel, thereby improving the ionic conductivity; (5) The adhesion of part of PAN subdivides the micropores in the membrane, and part of the large micropores will be divided into smaller micropores, optimizing the pore size distribution and increasing the uniformity of the pores, which will also improve the ionic conductivity. The fibers spun by solution mixing spinning will have uneven shrinkage everywhere, which will lead to uneven porosity, and PAN exists everywhere in each fiber, so the degree of fiber adhesion will increase greatly, which will adversely affect the increase of porosity and lead to a decrease in ionic conductivity.

[0041] Advantages:

[0042] (1) The preparation method of the fiber separator for lithium batteries of the present application can achieve the best concentration of spinning by separately configuring PAA and PAN monomer solutions, and there is no mutual interference between components before spinning;

[0043] (2) The preparation method of the fiber separator for lithium batteries of the present application, when electrospinning, uses two spinning ports to spin separately, and the separate spinning of PI and PAN has been very mature, and the best spinning voltage and collection distance can be selected without mutual interference;

[0044] (3) The preparation method of the fiber separator for lithium batteries of the present application is simple, only one additional spinning device is needed, and no other substances or equipment are added;

[0045] (4) The fiber separator for lithium batteries prepared by the method of the present application has significantly improved mechanical properties and better ionic conductivity than the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 SEM image of PAA / PAN nanofiber membrane before heat treatment of Example 3;

[0047] Figure 2 SEM image of PI / oPAN after heat treatment of Example 3;

[0048] Figure 3 SEM of PAN before heat treatment;

[0049] Figure 4 SEM of PAN treated at 300℃ for 2h;

[0050] Figure 5 SEM images of PAN treated at 300℃ for 4 hours;

[0051] Figure 6 SEM images of PAN treated at 400℃ for 2 hours;

[0052] Figure 7 This is a SEM image of the fiber separator for the lithium battery in Comparative Example 1. Detailed Implementation

[0053] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0054] The polyacrylonitrile (PAN) used in this invention is sourced from Beijing Bailingwei Technology Co., Ltd., with trade name 226749. Its SEM image before heat treatment is as follows: Figure 3 As shown.

[0055] The testing method used in this invention is as follows:

[0056] (1) Tensile strength: The tensile strength of the fiber separator for lithium batteries was tested using an Instron universal testing machine (Instron, 5967) at a rate of 20 mm / min and a gauge length of 20 mm.

[0057] (2) Ionic conductivity: The separator was placed between two stainless steel sheets and immersed in electrolyte (1M LiPF6, EC / DEC / DMC (V / V / V is 1 / 1 / 1)) to prepare a test battery. The bulk resistance data was obtained at room temperature with an amplitude of 10mV in the frequency range of 10 to 100kHz. The ionic conductivity (σ, mS / cm) of the fiber separator for lithium batteries was calculated according to the following formula.

[0058]

[0059] In the formula, d is the thickness of the diaphragm (cm), and R... b s is the bulk resistance (Ω), and s is the area of ​​the diaphragm (cm²). 2 ).

[0060] Example 1

[0061] A method for preparing a fiber separator for lithium batteries, comprising the following specific steps:

[0062] (1) first add diamino diphenyl ether into DMAc, stir at room temperature until completely dissolved to obtain a diamino diphenyl ether solution, then gradually add pyromellitic dianhydride into the diamino diphenyl ether solution according to a mass ratio of 6:3:1, and stir to form a polyamide acid spinning solution;

[0063] The mass fraction of pyromellitic dianhydride in the polyamide acid spinning solution is 12wt%, and the mass fraction of diamino diphenyl ether is 13wt%;

[0064] (2) add polyacrylonitrile into DMAc, stir at room temperature until completely dissolved to obtain a polyacrylonitrile spinning solution with a concentration of 10wt%;

[0065] (3) cross-spin the polyamide acid spinning solution obtained in step (1) and the polyacrylonitrile spinning solution obtained in step (2) respectively, that is, use two independent electrospinning devices to electrospin the polyamide acid spinning solution and the polyacrylonitrile spinning solution respectively, and then use the same collection roller to collect to obtain a PAA / PAN nanofiber membrane;

[0066] The volume ratio of the polyamide acid spinning solution to the polyacrylonitrile spinning solution is 1.2:0.9, and the process parameters of electrospinning are as follows:

[0067] For polyamide acid, the spinning voltage is 20kV, the distance between the spinneret and the collection roller is 16cm, and the advancing speed is 0.8mL / h;

[0068] For polyacrylonitrile, the spinning voltage is 15kV, the distance between the spinneret and the collection roller is 13cm, and the advancing speed is 0.8mL / h;

[0069] (4) roll the PAA / PAN nanofiber membrane obtained in step (3) to a density of 0.6g / cm 3 ;

[0070] (5) fix the PAA / PAN nanofiber membrane after roll processing in step (4) on an aluminum foil, heat in a muffle furnace at a temperature increasing rate of 10℃ / min from room temperature to 300℃ and keep for 2h to obtain a PI / oPAN nanofiber membrane, i.e. a fiber separator for lithium battery.

[0071] The prepared fiber separator for lithium battery is an electrospun PI / oPAN nanofiber membrane composed of PI fibers and oPAN fibers arranged in an interlaced and stacked manner, the average diameter of the PI fibers is 0.45μm, and the average diameter of the oPAN fibers is 0.14μm;

[0072] The average pore size of the fiber separator for lithium battery is 1.2μm, the porosity is 73.4%, the tensile strength is 22.4MPa, and the ionic conductivity is 3.65mS / cm.

[0073] Comparative Example 1

[0074] A preparation method of a fiber separator for lithium battery, which is substantially the same as that of Example 1, except that step (3) is specifically as follows:

[0075] The polyamide acid spinning solution obtained in step (1) and the polyacrylonitrile spinning solution obtained in step (2) are mixed in a volume ratio of 1:1, and then electrospun instead of cross spinning, and then collected by a collection roller to obtain a PAA / PAN nanofiber membrane.

[0076] The process parameters of electrospinning are as follows: the spinning voltage is 18 kV, the distance between the spinneret and the collection roller is 17 cm, and the advancing speed is 1 mL / h.

[0077] The fiber separator for lithium battery prepared has poor fiber formation, and the fibers are severely adhered to each other after imidization, as shown in FIG. 1. Figure 7

[0078] The fiber separator for lithium battery has a pore size of 0.8 pm, a porosity of 61%, a tensile strength of 5.3 MPa, and an ionic conductivity of 0.63 mS / cm.

[0079] Comparing Comparative Example 1 with Example 1, it can be seen that the tensile strength and ionic conductivity of the fiber separator for lithium battery prepared in Comparative Example 1 are both significantly smaller than those of Example 1. This is because in Comparative Example 1, each fiber is adhered, resulting in a smaller pore size and a lower porosity, and reducing the ionic conductivity. Moreover, after heat treatment, each fiber is reduced in mechanical strength due to the presence of about 50% PAN, and the adhesion effect is insufficient to compensate for the reduction in mechanical strength, resulting in a reduction in the overall film tensile strength.

[0080] Example 2

[0081] A preparation method of a fiber separator for lithium battery, the specific steps are as follows:

[0082] (1) First, add oxydianiline into DMAc, stir at room temperature until completely dissolved to obtain an oxydianiline solution, and then gradually add pyromellitic dianhydride into the oxydianiline solution according to a mass ratio of 6:3:1, and stir to form a polyamide acid spinning solution;

[0083] The mass fraction of pyromellitic dianhydride in the polyamide acid spinning solution is 14wt%, and the mass fraction of oxydianiline is 11wt%;

[0084] (2) Add polyacrylonitrile into DMAc, stir at room temperature until completely dissolved to obtain a polyacrylonitrile spinning solution with a concentration of 12wt%;

[0085] ​(3) respectively, the polyamide acid spinning solution obtained in step (1) and the polyacrylonitrile spinning solution obtained in step (2) are cross-spun, that is, using two independent electrospinning devices, the polyamide acid spinning solution and the polyacrylonitrile spinning solution are electrospun respectively, and then collected using the same collection roller to obtain a PAA / PAN nanofiber membrane;

[0086] The volume ratio of the polyamide acid spinning solution to the polyacrylonitrile spinning solution is 1.2:1, and the process parameters of electrospinning are as follows:

[0087] For polyamide acid, the spinning voltage is 20kV, the distance between the spinneret and the collection roller is 16.5cm, and the advancing speed is 1mL / h;

[0088] For polyacrylonitrile, the spinning voltage is 17kV, the distance between the spinneret and the collection roller is 14cm, and the advancing speed is 0.9mL / h;

[0089] (4) The PAA / PAN nanofiber membrane obtained in step (3) is subjected to roll pressing treatment, and the roll pressing density is 0.65g / cm 3 ;

[0090] (5) The PAA / PAN nanofiber membrane subjected to roll pressing treatment in step (4) is fixed on an aluminum foil, and is heated in a muffle furnace at a temperature increasing rate of 5℃ / min from room temperature to 250℃ and kept for 2h to obtain a PI / oPAN nanofiber membrane, that is, a fiber separator for lithium battery.

[0091] The prepared fiber separator for lithium battery is an electrospun PI / oPAN nanofiber membrane, which is composed of PI fibers and oPAN fibers arranged in an interlaced and stacked manner, the average diameter of the PI fibers is 0.48μm, and the average diameter of the oPAN fibers is 0.18μm.

[0092] The average pore size of the fiber separator for lithium battery is 1.1μm, the porosity is 72.9%, the tensile strength is 25.6MPa, and the ionic conductivity is 2.86mS / cm.

[0093] Example 3

[0094] A preparation method of a fiber separator for lithium battery, the specific steps are as follows:

[0095] (1) First, diamino diphenyl ether is added to DMAc, stirred at room temperature until completely dissolved to obtain a diamino diphenyl ether solution, and then pyromellitic dianhydride is gradually added to the diamino diphenyl ether solution according to a mass ratio of 6:3:1, and stirred to form a polyamide acid spinning solution;

[0096] The mass fraction of pyromellitic dianhydride in the polyamide acid spinning solution is 13wt%, and the mass fraction of diamino diphenyl ether is 12wt%;

[0097] (2) polyacrylonitrile was added into DMAc and stirred at room temperature until completely dissolved to obtain a polyacrylonitrile spinning solution with a concentration of 10 wt%;

[0098] (3) polyamide acid spinning solution obtained in step (1) and polyacrylonitrile spinning solution obtained in step (2) were cross-spun, i.e. polyamide acid spinning solution and polyacrylonitrile spinning solution were electrospun respectively using two independent electrospinning devices, and then collected using the same collection roller to obtain PAA / PAN nanofiber membrane, SEM image of which is shown in Figure 1 ;

[0099] wherein the volume ratio of polyamide acid spinning solution to polyacrylonitrile spinning solution was 1:1, and the process parameters of electrospinning were as follows:

[0100] for polyamide acid, the spinning voltage was 18 kV, the distance between the spinneret and the collection roller was 18 cm, and the advancing speed was 1 mL / h;

[0101] for polyacrylonitrile, the spinning voltage was 16 kV, the distance between the spinneret and the collection roller was 15 cm, and the advancing speed was 1 mL / h;

[0102] (4) PAA / PAN nanofiber membrane obtained in step (3) was subjected to roll pressing treatment, and the density after roll pressing was 0.6 g / cm 3 ;

[0103] (5) PAA / PAN nanofiber membrane after roll pressing treatment in step (4) was fixed on an aluminum foil, and was heated in a muffle furnace at a temperature rising rate of 10 ℃ / min from room temperature to 300 ℃ and kept for 2 h to obtain PI / oPAN nanofiber membrane, i.e. fiber separator for lithium battery, SEM image of which is shown in Figure 2 .

[0104] The prepared fiber separator for lithium battery was electrospun PI / oPAN nanofiber membrane, which was composed of PI fibers and oPAN fibers arranged in an interlaced and stacked manner, the average diameter of PI fibers was 0.5 μm, and the average diameter of oPAN fibers was 0.2 μm.

[0105] The average pore size of the fiber separator for lithium battery was 1 μm, the porosity was 72.2%, the tensile strength was 35.3 MPa, and the ionic conductivity was 2.05 mS / cm.

[0106] As can be seen from 1-3, the shrinkage of PAN and PI is not the same during heat treatment. The diameter of PAN is about 0.3 microns before heat treatment, and about 0.24 microns after heat treatment, which is reduced by 20%. The diameter of PI is about 0.8 microns before heat treatment, and about 0.48 microns after heat treatment, which is reduced by 40%. The fibers spun by solution mixing will have uneven shrinkage, which will lead to uneven pores. PAN exists in each part of the fiber, and the degree of fiber adhesion will increase, which will adversely affect the increase of pores.

[0107] Example 4

[0108] A preparation method of a fiber separator for lithium batteries, the specific steps are as follows:

[0109] (1) First, add diamino diphenyl ether into DMAc, stir at room temperature until completely dissolved to obtain a diamino diphenyl ether solution, then gradually add pyromellitic dianhydride into the diamino diphenyl ether solution according to a mass ratio of 6:3:1, and stir to form a polyamic acid spinning solution;

[0110] The mass fraction of pyromellitic dianhydride in the polyamic acid spinning solution is 12.5wt%, and the mass fraction of diamino diphenyl ether is 12.5wt%;

[0111] (2) Add polyacrylonitrile into DMAc, stir at room temperature until completely dissolved to obtain a polyacrylonitrile spinning solution with a concentration of 11.5wt%;

[0112] (3) Cross spinning of the polyamic acid spinning solution obtained in step (1) and the polyacrylonitrile spinning solution obtained in step (2) is carried out, that is, using two independent electrospinning devices, electrospinning of the polyamic acid spinning solution and the polyacrylonitrile spinning solution is carried out respectively, and then using the same collection roller to collect to obtain a PAA / PAN nanofiber membrane;

[0113] Among them, the volume ratio of polyamic acid spinning solution to polyacrylonitrile spinning solution is 0.9:1, and the process parameters of electrospinning are as follows:

[0114] For polyamic acid, the spinning voltage is 19kV, the distance between the spinneret and the collection roller is 17.5cm, and the advancing speed is 0.9mL / h;

[0115] For polyacrylonitrile, the spinning voltage is 15kV, the distance between the spinneret and the collection roller is 13cm, and the advancing speed is 0.8mL / h;

[0116] (4) The PAA / PAN nanofiber membrane obtained in step (3) is subjected to roll pressing treatment, and the density is 0.6g / cm 3 ;

[0117] (5) The PAA / PAN nanofiber membrane after the rolling treatment in step (4) is fixed on an aluminum foil, and is heated in a muffle furnace at a temperature increasing rate of 5 ℃ / min from room temperature to 280 ℃ and kept for 2 h to obtain a PI / oPAN nanofiber membrane, i.e. a fiber separator for lithium batteries.

[0118] The fiber separator for lithium batteries prepared is an electrospun PI / oPAN nanofiber membrane composed of PI fibers and oPAN fibers arranged in an interlaced and stacked manner, the average diameter of the PI fibers is 0.52 μm, and the average diameter of the oPAN fibers is 0.22 μm.

[0119] The fiber separator for lithium batteries has an average pore diameter of 1 μm, a porosity of 71.5%, a tensile strength of 34.1 MPa, and an ionic conductivity of 1.94 mS / cm.

[0120] Example 5

[0121] A method for preparing a fiber separator for lithium batteries, the specific steps are as follows:

[0122] (1) First, diamino diphenyl ether is added to DMAc, stirred at room temperature until completely dissolved to obtain a diamino diphenyl ether solution, and then pyromellitic dianhydride is gradually added to the diamino diphenyl ether solution according to a mass ratio of 6:3:1, and stirred to form a polyamide acid spinning solution;

[0123] The mass fraction of pyromellitic dianhydride in the polyamide acid spinning solution is 13.5 wt%, and the mass fraction of diamino diphenyl ether is 12 wt%;

[0124] (2) Polyacrylonitrile is added to DMAc and stirred at room temperature until completely dissolved to obtain a polyacrylonitrile spinning solution with a concentration of 11 wt%;

[0125] (3) The polyamide acid spinning solution obtained in step (1) and the polyacrylonitrile spinning solution obtained in step (2) are cross-spun, i.e. using two independent electrospinning devices, the polyamide acid spinning solution and the polyacrylonitrile spinning solution are electrospun respectively, and then collected using the same collection roller to obtain a PAA / PAN nanofiber membrane;

[0126] Among them, the volume ratio of the polyamide acid spinning solution to the polyacrylonitrile spinning solution is 1:0.9, and the process parameters of electrospinning are as follows:

[0127] For polyamide acid, the spinning voltage is 18 kV, the distance between the spinneret and the collection roller is 18 cm, and the advancing speed is 0.95 mL / h;

[0128] For polyacrylonitrile, the spinning voltage is 16 kV, the distance between the spinneret and the collection roller is 14 cm, and the advancing speed is 0.9 mL / h;

[0129] (4) The PAA / PAN nanofiber membrane obtained in step (3) is subjected to roller pressing treatment, and is pressed to a density of 0.65 g / cm 3 ;

[0130] (5) The PAA / PAN nanofiber membrane subjected to roller pressing treatment in step (4) is fixed on an aluminum foil, and is heated in a muffle furnace at a temperature increasing rate of 10 ℃ / min from room temperature to 320 ℃ and kept for 2 h to obtain a PI / oPAN nanofiber membrane, i.e. a fiber separator for lithium battery.

[0131] The fiber separator for lithium battery prepared is an electrospun PI / oPAN nanofiber membrane composed of PI fibers and oPAN fibers arranged in an interlaced and stacked manner, the average diameter of the PI fibers is 0.53 μm, and the average diameter of the oPAN fibers is 0.23 μm.

[0132] The fiber separator for lithium battery has an average pore size of 0.9 μm, a porosity of 68.7%, a tensile strength of 32.5 MPa, and an ionic conductivity of 1.82 mS / cm.

[0133] Example 6

[0134] A preparation method of a fiber separator for lithium battery, the specific steps are as follows:

[0135] (1) First, diamino diphenyl ether is added to DMAc, stirred at room temperature until completely dissolved to obtain a diamino diphenyl ether solution, and then pyromellitic dianhydride is gradually added to the diamino diphenyl ether solution according to a mass ratio of 6:3:1, and stirred to form a polyamide acid spinning solution;

[0136] The mass fraction of pyromellitic dianhydride in the polyamide acid spinning solution is 13wt%, and the mass fraction of diamino diphenyl ether is 11.5wt%;

[0137] (2) Polyacrylonitrile is added to DMAc and stirred at room temperature until completely dissolved to obtain a polyacrylonitrile spinning solution with a concentration of 12wt%;

[0138] (3) The polyamide acid spinning solution obtained in step (1) and the polyacrylonitrile spinning solution obtained in step (2) are cross-spun, i.e. using two independent electrospinning devices, the polyamide acid spinning solution and the polyacrylonitrile spinning solution are electrospun respectively, and then collected using the same collection roller to obtain a PAA / PAN nanofiber membrane;

[0139] Among them, the volume ratio of the polyamide acid spinning solution to the polyacrylonitrile spinning solution is 1.1:1, and the process parameters of electrospinning are as follows:

[0140] For polyamide acid, the spinning voltage is 18kV, the distance between the spinneret and the collection roller is 18cm, and the advancing speed is 0.9mL / h;

[0141] For polyacrylonitrile, the spinning voltage was 17 kV, the distance between the spinneret and the collection roller was 15 cm, and the advancing speed was 1 mL / h;

[0142] (4) The PAA / PAN nanofiber membrane obtained in step (3) was subjected to a rolling treatment to a density of 0.55 g / cm 3 ;

[0143] (5) The PAA / PAN nanofiber membrane subjected to the rolling treatment in step (4) was fixed on an aluminum foil, and was heated in a muffle furnace at a temperature increasing rate of 15 °C / min from room temperature to 300 °C and maintained for 2 h to obtain a PI / oPAN nanofiber membrane, i.e., a fiber separator for lithium batteries.

[0144] The fiber separator for lithium batteries obtained was an electrospun PI / oPAN nanofiber membrane composed of PI fibers and oPAN fibers arranged in an interlaced and stacked manner, the average diameter of the PI fibers was 0.55 μm, and the average diameter of the oPAN fibers was 0.26 μm.

[0145] The fiber separator for lithium batteries had an average pore diameter of 0.8 μm, a porosity of 64.8%, a tensile strength of 30.8 MPa, and an ionic conductivity of 1.78 mS / cm.

Claims

1. A method for producing a fibrous separator for lithium batteries, characterized by, The polyamide acid spinning solution and the polyacrylonitrile spinning solution are cross-spun to obtain a PAA / PAN nanofiber membrane, then the PAA / PAN nanofiber membrane is subjected to roll pressing treatment, and finally the PAA / PAN nanofiber membrane subjected to the roll pressing treatment is subjected to heating treatment to obtain a PI / oPAN nanofiber membrane, i.e. the fiber separator for lithium batteries; The PAA / PAN nanofiber membrane is obtained by cross-spinning the polyamide acid spinning solution and the polyacrylonitrile spinning solution, which refers to using two independent electrospinning devices to electrospin the polyamide acid spinning solution and the polyacrylonitrile spinning solution respectively, and using the same collection roller to collect the PAA / PAN nanofiber membrane. The heating treatment temperature is 250-350℃. The fiber separator for lithium batteries is an electrospun PI / oPAN nanofiber membrane. The PI / oPAN nanofiber membrane is composed of polyimide fibers and pre-oxidized polyacrylonitrile fibers arranged in an interlaced and stacked manner, the average diameter of the polyimide fibers is 0.45-0.55μm, and the average diameter of the pre-oxidized polyacrylonitrile fibers is 0.14-0.26μm. The tensile strength of the fiber separator for lithium batteries is 22.4-35.3MPa, and the ionic conductivity is 2.86-3.65mS / cm.

2. The method for preparing a fiber separator for lithium batteries according to claim 1, characterized in that, The average pore size of the fiber separator for lithium batteries is 0.8-1.2μm, and the porosity is 64.8-73.4%.

3. The method for preparing a fiber separator for lithium batteries according to claim 1, characterized in that, The specific steps are as follows: (1) first, diamino diphenyl ether is added to DMAc and stirred until completely dissolved to obtain a diamino diphenyl ether solution, then pyromellitic dianhydride is added to the diamino diphenyl ether solution in batches, and stirred to form a polyamide acid spinning solution; (2) polyacrylonitrile is added to DMAc and stirred until completely dissolved to obtain a polyacrylonitrile spinning solution; (3) the polyamide acid spinning solution obtained in step (1) and the polyacrylonitrile spinning solution obtained in step (2) are electrospun respectively, and the same collection roller is used to collect the PAA / PAN nanofiber membrane; (4) The PAA / PAN nanofiber membrane obtained in step (3) is subjected to roll pressing treatment, and the roll pressing is performed to a density of 0.6±0.05 g / cm 3 ; (5) the PAA / PAN nanofiber membrane subjected to the roll pressing treatment in step (4) is fixed on an aluminum foil, heated to 250-350℃ at a temperature rising rate of 10±5℃ / min in a muffle furnace and kept for 2h to obtain a PI / oPAN nanofiber membrane, i.e. the fiber separator for lithium batteries.

4. The method of claim 3, wherein the lithium battery fiber separator is prepared by the steps of: In step (1), the pyromellitic dianhydride is added to the diamino diphenyl ether solution in batches, which means that the pyromellitic dianhydride is gradually added to the diamino diphenyl ether solution according to a mass ratio of 6:3:

1.

5. The method for preparing a fiber separator for lithium batteries according to claim 3, characterized in that, In step (1), the mass fraction of pyromellitic dianhydride in the polyamide acid spinning solution is 12-14wt%, and the mass fraction of diamino diphenyl ether is 11-13wt%.

6. The method for preparing a fiber separator for lithium batteries according to claim 3, characterized in that, In step (2), the concentration of the polyacrylonitrile spinning solution is 10-12wt%.

7. The method for preparing a fiber separator for lithium batteries according to claim 3, characterized in that, In step (3), the volume ratio of the polyamide acid spinning solution to the polyacrylonitrile spinning solution is 0.9-1.2:0.9-1.

8. The method for preparing a fiber separator for lithium batteries according to claim 3, characterized in that, In step (3), the process parameters of electrospinning are as follows: For the polyamide acid, the spinning voltage is 18-20kV, the distance between the spinneret and the collection roller is 16-18cm, and the advancing speed is 0.8-1mL / h; For polyacrylonitrile, the spinning voltage is 15-17 kV, the distance between the spinneret and the collecting roller is 13-15 cm, and the advancing speed is 0.8-1 mL / h.

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