WO2023159823A1

WO2023159823A1 - Porous fiber composite separator and preparation method therefor

Info

Publication number: WO2023159823A1
Application number: PCT/CN2022/100731
Authority: WO
Inventors: 庄志; 杨登科; 李堃; 彭锟; 宫晓明; 王培勇; 冶成良; 程跃
Original assignee: 上海恩捷新材料科技有限公司
Priority date: 2022-02-24
Filing date: 2022-06-23
Publication date: 2023-08-31
Also published as: CN114583384B; CN114583384A

Abstract

A porous fiber composite separator, comprising: a structural fiber, formed by spinning of a structural resin; and a functional fiber, formed by spinning of a functional resin, and cross-linked and wound with the functional fiber. The functional fiber has a carbonyl or cyano functional group. The structural resin comprises any one or more of polymethyl methacrylate, polystyrene, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene terephthalate, polyurethane, and polyester.

Description

A kind of porous fiber composite diaphragm and preparation method thereof

technical field

The invention belongs to the field of lithium battery diaphragms, in particular to a porous fiber composite diaphragm.

Background technique

As one of the four key materials, the lithium battery separator not only needs to effectively block the direct contact between the positive and negative electrodes of the battery, but also needs to have good ion conductivity to allow lithium ions to pass through quickly during charging and discharging. The performance of the separator determines the interface structure and internal resistance of the lithium battery, which in turn affects the key characteristics of the battery such as capacity, cycle life, and charge-discharge current density. Therefore, the improvement of the performance of the separator plays an important role in improving the overall performance of the lithium-ion battery. effect. As the market continues to put forward new requirements for the energy density and rate performance of lithium batteries, the demand for separators with good ionic conductivity and high liquid absorption and retention has also been applied. Current studies have shown that increasing the porosity of the membrane can effectively improve the ionic conductivity and liquid absorption and retention performance of the membrane, but how to further improve the ionic conductivity of the porous membrane has become a new area of concern for technicians.

Contents of the invention

An object of the present invention is to provide a porous fiber composite diaphragm, which includes: a structural fiber formed by spinning a structural resin; and a functional fiber formed by spinning a functional resin, and the functional fiber The fibers are interlinked and intertwined, wherein the functional fibers have carbonyl or cyano functional groups, and the structural resin contains polymethyl methacrylate, polystyrene, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene terephthalic acid Any one or more of glycol esters, polyurethanes, and polyesters.

In the porous fiber composite diaphragm as described above, the functional resin includes any one or more of polyacrylonitrile, polyarylether sulfone ketone, polypropylene oxide, polylactic acid, carboxymethyl cellulose, and polyacrylamide.

Another object of the present invention is to provide a method for preparing a porous fiber composite diaphragm, the method comprising: a first solution preparation step: uniformly mixing the structural resin, a first solvent and a second solvent to prepare a first solution solution; the second solution preparation step: uniformly mix the functional resin, a third solvent and the second solvent to prepare a second solution; spinning step: load the first solution with a first syringe, and use the second Two syringes are installed in the second solution, spraying the first solution at a first feed rate to form the structural fibers and spraying the second solution at a second feed rate to form the function in an electrostatic field, respectively Fiber; film forming step: the structural fiber and the functional fiber are cross-linked and intertwined on a substrate to form the porous fiber composite membrane.

As an example, the speed ratio of the first feed rate to the second feed rate is 1:1 to 1:5.

As an example, said first feed rate is between 0.1 ml/h and 10.0 ml/h; said second feed rate is between 0.1 ml/h and 10.0 ml/h.

As an example, the electrostatic field is formed by a voltage between 5.0 kV and 20.0 kV.

As an example, the first injector or the second injector is spaced from the substrate by a specific feeding distance, and the feeding distance is between 100 mm and 200 mm.

As an example, the first solvent includes one of dimethylsulfoxide, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and hexafluoropropanol. one or more; the second solvent includes one or more of ethanol, propanol, dimethyl carbonate; preferably, the structural resin: the first solvent: the second solvent For (0.5g to 2.0g): (5.0ml to 9.0ml): (1.0ml to 5.0ml).

As an example, the third solvent includes one of dimethylsulfoxide, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and hexafluoropropanol. one or more; the fourth solvent includes one or more of ethanol, propanol, and methylene chloride dimethyl carbonate; preferably, the functional resin: the first solvent: the second solvent For (0.5g to 2.0g): (5.0ml to 9.0ml): (1.0ml to 5.0ml).

As an example, the structural resin is polymethyl methacrylate and the functional resin is polyacrylonitrile.

As an example, the first solvent is dimethylsulfoxide, the second solvent is dichloromethane, the third solvent is tetrahydrofuran, and the fourth solvent is dichloromethane.

Further, the preparation method further includes: a heat treatment step: collecting the porous fiber composite diaphragm from the base material and placing it on a substrate, and heat treating the porous fiber composite diaphragm at a temperature.

As an example, the substrate includes a glass plate or a plastic plate.

As an example, the temperature is between 100°C and 150°C.

In the porous fiber composite diaphragm provided by the present invention and its preparation method, solutions are respectively prepared with functional resins containing carbonyl or cyano functional groups and structural resins with high mechanical strength, and the prepared solutions are respectively added to the electrospinning equipment. Different spinning nozzles are used to spin at the same time; under the interference of the electrostatic field between different nozzles, in the process of spinning to form functional fibers and structural fibers, the two are entangled with each other, so that the two fibers are evenly distributed and alternate. The intertwined fibers are subsequently formed into a membrane.

The beneficial effect obtained by the above method of the present invention is: the two kinds of resin fibers are cross-linked and entangled during the spinning process, forming a large number of pore structures, so that the finished diaphragm at the rear end has good wetting performance and liquid absorption and liquid retention performance; In addition, the cross-linking of the structural resin and the functional resin makes the porous fiber composite separator have good tensile strength, and the carbonyl or cyano group in the functional resin can interact with the solvent molecules in the electrolyte to improve the wettability of the separator to the electrolyte. Reducing the interface resistance can also enhance the ion conductivity, which is conducive to the rapid passage of lithium ions through the separator during charging and discharging, reducing the loss of lithium ions, and effectively improving the cycle performance and rate performance of lithium batteries.

Detailed ways

In order to further understand the present invention, the preferred solutions of the present invention will be described below in combination with specific embodiments, so as to facilitate those skilled in the art to understand the present invention.

One embodiment of the present invention is a porous fiber composite diaphragm, which includes: a structural fiber, formed by spinning a structural resin; and a functional fiber, formed by spinning a functional resin, and the functional fiber The fibers are interlinked and intertwined, wherein the functional fibers have carbonyl or cyano functional groups.

Preferably, the structural resin comprises polymethyl methacrylate (Poly (methyl methacrylate), PMMA), polystyrene (Polystyrene, PS), polyvinylidene difluoride (Polyvinylidene difluoride, PVDF), polytetrafluoroethylene (Polytetrafluoroethylene , PTFE), polyethylene terephthalate (Polyethylene terephthalate, PET), polyurethane (Polyurethane, PUR), polyester (Polyester, PE) in any one or more; More preferably, described structure The resin is polymethyl methacrylate.

Preferably, the functional resin comprises polyacrylonitrile (Polyacrylonitrite, PAN), polyarylether sulfone ketone (polyetheretherketon, PEEK), polypropylene oxide (Poly[oxy(methyl-1,2-ethanediyl)]), polylactic acid (Polylactic Acid, PLA), carboxymethyl cellulose (Carboxymethyl Cellulose, CMC), polyacrylamide (polyacrylamide, PAM) any one or more; More preferably, described functional resin is polyacrylonitrile.

Specifically, the carbonyl or cyano group contained in the functional resin can inhibit the anion from penetrating the separator in back-end applications; for example, when the electrolyte contains carbonate, the carbonyl or cyano group can dissolve the carbonate The intermolecular interactions repel negatively charged carbonate anions, thereby inhibiting the ability of carbonate anions to pass through the separator, increasing the migration rate of cations, and enhancing the wettability of the separator to the electrolyte.

Another embodiment of the present invention is a preparation method of a porous fiber composite diaphragm, used to prepare the aforementioned porous fiber composite diaphragm; please refer to Figure 1, the preparation method includes:

S1) Step of preparing the first solution: uniformly mixing the structural resin, a first solvent and a second solvent to prepare a first solution;

S2) second solution preparation step: uniformly mixing the functional resin, a third solvent and a fourth solvent to prepare a second solution;

S3) spinning step: loading the first solution with a first syringe, loading the second solution with a second syringe, spraying the first solution at a first feed rate in an electrostatic field respectively to form the said structural fibers and spraying said second solution at a second feed rate to form said functional fibers;

S4) Membrane forming step: the structural fibers and the functional fibers are cross-linked and intertwined on a substrate to form the porous fiber composite membrane.

As an example, in the spinning step, there is a specific feeding distance (L) between the first syringe or the second syringe and the substrate, and the feeding distance (L) is between 100mm and 200mm between.

For example, the electrospinning method is implemented in the spinning step, and the spinning device (1) used can be listed as a receiving roll (13) with double injectors, and the double injectors can be along the long axis of the receiving roll ( The mode that Ax) direction moves left and right carries out spinning; Please refer to Fig. 2, is the schematic diagram of an exemplary spinning device (1), and in this example, spinning device (1) comprises the first injector (11), the second The syringe (12) and the receiving roller (13), specifically, contain the first solution (A) in the first syringe (11), and the second solution B in the second syringe (12), and are respectively set to the first solution (A). The feed rate and the second feed rate are transmitted toward the receiving roller (13) to form structural fibers (A1) and functional fibers (B1) respectively, and the receiving roller (13) rotates 360 degrees with the major axis Ax as the axis, and the structural fibers (A1 ) and functional fibers (B1) are cross-linked and wound in the feeding space (Sp) and gradually attached to the receiving roller; further, the first injector (11) and the second injector (12) move left and right along the receiving roller, which can Make the structural fiber (A1) and the functional fiber (B1) cross-linked and entwined more uniformly, so that the pore distribution of the porous fiber composite diaphragm produced later is more uniform; please refer to Figure 3 again, which is an exemplary spinning device 2 In this example, the difference from the spinning device (1) is that the first injector 21 and the second injector 22 are relatively arranged on both sides of the long axis (Ax) of the receiving roll; The left and right movement modes of the first syringe (11) and the second syringe (12) can be synchronous left and right movement, or staggered left and right movement, and the mode is not particularly limited; state for spinning.

As an example, the substrate may be formed of glass or plastic; preferably, the substrate is covered with a metal layer, and the metal layer is more preferably aluminum foil.

As an example, the first solvent includes dimethyl sulfoxide (Dimethyl sulfoxide, DMSO), tetrahydrofuran (Tetrahydrofuran, THF), N,N-dimethylformamide (Dimethylformamide, DMF), N,N-dimethyl One or more of acetamide (Dimethylacetamide, DMAc), N-methylpyrrolidone (N-Methyl-2-pyrrolidone, NMP), hexafluoropropanol (Hexafluoroisopropanol, HFIP); the second solvent includes ethanol ( One or more in Ethanol, EtOH), propanol (Propanol, PrOH), dichloromethane (Methylene chloride, DCM), dimethyl carbonate; Preferably, described structural resin: described first solvent: described The preparation ratio of the second solvent is (0.5g to 2.0g):(5.0ml to 9.0ml):(1.0ml to 5.0ml), more preferably 0.5g:8.0ml:2.0ml.

As an example, the third solvent includes one of dimethylsulfoxide, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and hexafluoropropanol. one or more; the fourth solvent includes one or more of ethanol, propanol, and dimethyl carbonate; preferably, the functional resin: the third solvent: the fourth solvent (0.5g to 2.0g): (5.0ml to 9.0ml): (1.0ml to 5.0ml); preferably, the preparation ratio of the structural resin: the first solvent: the second solvent is 0.5g :8.0ml:2.0ml, more preferably 0.5g:8.0ml:2.0ml.

As a preferred example, the preparation method further includes:

S5) heat treatment step: collecting the porous fiber composite membrane from the base material and placing it on a substrate, and heat treating the porous fiber composite membrane at a temperature.

As an example, the substrate may be a glass or plastic plate.

As an example, the temperature ranges from 100°C to 150°C, more preferably 120°C; there is no special limitation on the drying environment or device, as long as it can control the ambient temperature within the temperature range, it can be used to dry porous Fiber composite membrane, such as heating and drying devices such as ovens and ovens.

Several examples will be enumerated below to further demonstrate the technical effects achieved by the porous fiber composite membrane and its preparation method provided by the present invention.

Example 1

1) Preparation of structural resin solution: The mixture of PMMA resin, dimethyl sulfoxide and dichloromethane is prepared into a uniform structural resin solution, wherein the preparation ratio of PMMA: dimethyl sulfoxide: dichloromethane is 0.5g: 8.0 ml: 2.0ml;

2) Preparation of functional resin solution: prepare a mixture of PAN resin, tetrahydrofuran and carbon dichloride to form a uniform functional resin solution, wherein the preparation ratio of PAN: tetrahydrofuran: dichloromethane is 0.5g: 8.0ml: 2.0ml;

3) Electrospinning: Use two clean syringes to absorb the structural resin solution and the functional resin solution respectively; adjust the positive and negative high-voltage power supply to the range of 5.0kV to 20.0kV, and adjust the feeding distance between the syringe and the receiving roller to 100mm to 200mm interval; the surface of the aforementioned receiving roller is covered with a layer of aluminum foil; set the feeding rate of the syringe and start to pressure-feed the structural resin solution and the functional resin solution for electrospinning, and the feeding rate ratio is 1:1; under the action of the electric field, the structural resin solution and functional resin solution to form structural fibers and functional fibers respectively;

4) Film formation: structural fibers and functional fibers are cross-linked and wound on the aluminum foil on the surface of the receiving roller to form a layer of fiber film;

5) Heat treatment: The fiber membrane was peeled off from the aluminum foil, then sandwiched between glass plates and placed in an oven at 120°C for heat treatment for 1 hour to obtain a porous fiber composite separator.

Example 2

The steps are the same as in Example 1, except that the feeding rate ratio is 1:3.

Example 3

The steps are the same as in Example 1, the difference is that the feeding rate ratio is 1:5.

Example 4

Step is with embodiment 1, difference is:

The ratio of PMMA: dimethyl sulfoxide: dichloromethane is 1.0g: 8.0ml: 2.0ml;

PAN: Tetrahydrofuran: Dichloromethane The preparation ratio is 1.0g: 8.0ml: 2.0ml;

The feed rate ratio is 1:5.

Example 5

Step is with embodiment 1, difference is:

The preparation ratio of PMMA: dimethyl sulfoxide: dichloromethane is 2.0g: 8.0ml: 2.0ml;

PAN: Tetrahydrofuran: Dichloromethane The preparation ratio is 2.0g: 8.0ml: 2.0ml;

The feed rate ratio is 1:5.

Comparative example 1

The procedure is the same as that in Example 1, except that both syringes absorb the structural resin solution for spinning to obtain a porous fiber membrane.

Comparative example 2

The steps are the same as in Example 1, except that both syringes draw the functional resin solution for spinning to obtain a porous fiber membrane.

The porosity, liquid absorption rate, liquid retention rate, tensile strength, ion conductivity and other properties of the fiber separator obtained in the above-mentioned Examples 1 to 5 and Comparative Example 1 and Comparative Example 2 were tested.

The specific test method is described as follows:

Porosity test

Calculate the void volume of the diaphragm occupied by liquid by measuring the mass difference before and after the diaphragm is infiltrated as the porosity of the diaphragm. The specific formula is as follows:

Among them, m ₁ is the mass of the sample before immersion, m ₂ is the mass of the sample after immersion, the selected solvent is n-butanol, and V ₀ is the apparent volume of the diaphragm.

Liquid Absorption Determination

The solvent is n-butanol, and the quality difference of the diaphragm before and after immersion is used for determination. The specific formula is as follows:

Among them, A% is the liquid absorption rate of the diaphragm, _m1 is the mass of the sample before immersion, and m2 is the mass of the sample after immersion.

Electrolyte liquid absorption rate and liquid retention rate

Cut the obtained composite film into a sample of 2×2 cm, dry it and weigh it, soak the weighed dry film (W ₀ ) in the LiPF6 electrolyte, take it out after 2 hours, and wipe off the excess electrolyte on the surface of the diaphragm with filter paper. The mass of the wet film is weighed after the solution is added, which is recorded as W _x1 , and the weight after saturated liquid absorption is recorded as W ₁ ; finally, the diaphragm soaked in the electrolyte is placed in an oven at 50°C for 1 hour, and the mass of the diaphragm is weighed, which is recorded as W _x2 ; The specific formulas of the liquid absorption rate and liquid retention rate of the diaphragm are as follows:

Tensile Strength Test

The equipment is tested by Shanghai Xiangjie XJ8108C tensile machine.

Electrochemical test :

The obtained composite film was cut into small discs with a diameter of 19 mm by a punching machine, assembled into a battery in a glove box, and electrochemically tested to measure the ionic conductivity. The equipment used was the Zennium electrochemical workstation of ZAHNER in Germany, and the frequency range of the measurement was 0.01Hz to 100KHz, the amplitude is 0.001V.

The results of the above-mentioned tests are listed in Table 1; as can be seen from Table 1, the porosity of the PMMA porous fiber membrane of a single component in Comparative Example 1 is not high, and cannot meet the high ion conductivity requirement. Although the PAN porous fiber membrane has higher porosity and liquid absorption rate, due to the low tensile strength of the membrane, the membrane leaks during use, the liquid retention rate and ion conductivity are not high, and cannot meet the high ion conductivity requirements.

See again embodiment 1 to embodiment 5, except that the tensile strength of membrane increases (56.0 to 69.0MPa) along with the content of PAN, under the condition that PMMA and PAN content decrease synchronously in spinning solution, The porosity (69.0 to 85.0%), liquid absorption rate (320 to 501%), and liquid retention rate (66.4 to 73.8%) of the separator are improved instead, which reduces the internal resistance of the separator, thereby improving the ion conductivity of the lithium-ion battery Rate (2.94 to 3.66mS/cm), so that the battery has better cycle performance and charge-discharge rate in use.

Table 1

More specifically, after Example 1 was compared with Comparative Example 1 and Comparative Example 2, unexpected technical effects were produced; under the expectation of addition, it was implemented with the feed rate ratio of 1:1, and Example 1 The technical effects obtained can be estimated as the average value achieved in Comparative Example 1 and Comparative Example 2, which are porosity porosity 69.5%, liquid absorption rate 430%, liquid retention rate 47.65%, tensile strength 50.0MPa, ion The electrical conductivity is 2.50mS/cm; yet, the technical effects actually harvested in Example 1 are significantly greater than the expected effects, respectively reaching 77.0% porosity, 465% liquid absorption, 62.5% liquid retention, 73.0% tensile strength and The ion conductivity is 3.30mS/cm; obviously, under the cross-linking and entanglement of the structural resin fiber and the functional resin fiber, there is a synergistic effect between them, which significantly improves the functionality of the porous fiber composite membrane, especially the ion conductivity The improvement of the rate is the most significant, achieving better cycle performance and higher charge-discharge rate.

To sum up, the porous fiber composite diaphragm provided by the present invention and the preparation method thereof are respectively configured with a structural resin with high mechanical strength and a functional resin containing carbonyl or cyano functional groups, and then through the electrospinning method, the The two are spun to generate structural fibers and functional fibers respectively, which are interlinked and intertwined, evenly distributed and produce a synergistic effect, so that the subsequent porous fiber composite diaphragm has several excellent functions:

First, the two resin fibers are cross-linked and intertwined during the spinning process, resulting in a large pore structure, which improves the wetting performance and liquid absorption and liquid retention performance of the rear-end finished diaphragm.

Second, the cross-linking of the two resin fibers makes the separator have good tensile strength, which is more reliable in the packaging of the battery liquid, and avoids the risk of battery liquid leakage during use.

Third, the carbonyl or cyano group in the functional resin can interact with the solvent molecules in the electrolyte during the charging and discharging process, which further improves the wettability of the separator to the electrolyte, thereby reducing the interface resistance and enhancing the ionic strength. The conductivity is conducive to the rapid passage of lithium ions through the separator, reducing the loss of lithium ions, and can effectively improve the cycle performance and rate performance of lithium batteries.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be considered For the scope of the present invention.

Claims

A porous fiber composite membrane comprising:

a structural fiber formed by spinning a structural resin; and

A functional fiber is formed by spinning a functional resin, cross-linked and entwined with the functional fiber, wherein the functional fiber has a carbonyl or cyano functional group, and the structural resin is composed of polymethyl methacrylate, Any one or more of polystyrene, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene terephthalate, polyurethane, polyester.
The porous fiber composite membrane according to claim 1, wherein the functional resin comprises polyacrylonitrile, polyarylether sulfone ketone, polypropylene oxide, polylactic acid, carboxymethyl cellulose, polyacrylamide Any one or more.
The porous fiber composite diaphragm as claimed in claim 1 or 2, its preparation method comprises:

The first solution preparation step: uniformly mixing the structural resin, a first solvent and a second solvent to prepare a first solution;

The second solution preparation step: uniformly mixing the functional resin, a third solvent and a fourth solvent to prepare a second solution;

spinning step: loading the first solution with a first syringe, loading the second solution with a second syringe, spraying the first solution respectively at a first feed rate in an electrostatic field to form the structure fibers and spraying the second solution at a second feed rate to form the functional fibers;

Membrane forming step: the structural fibers and the functional fibers are interlinked and intertwined on a substrate to form the porous fiber composite membrane.
The porous fiber composite membrane according to claim 3, wherein the speed ratio of the first feed rate to the second feed rate is 1:1 to 1:5.
The porous fiber composite membrane according to claim 3 or 4, wherein the first solvent comprises dimethyl sulfoxide, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide One or more of amides, N-methylpyrrolidone, and hexafluoropropanol; the second solvent includes one or more of ethanol, propanol, methylene chloride, and dimethyl carbonate.
The porous fiber composite membrane according to claim 5, wherein the third solvent comprises dimethyl sulfoxide, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, One or more of N-methylpyrrolidone and hexafluoropropanol; the fourth solvent includes one or more of ethanol, propanol, methylene chloride, and dimethyl carbonate.
The porous fiber composite membrane according to claim 6, wherein the structural resin is polymethyl methacrylate, the functional resin is polyacrylonitrile; the first solvent is dimethyl sulfoxide, and the The second solvent is dichloromethane; the third solvent is tetrahydrofuran, and the fourth solvent is dichloromethane.
The porous fiber composite membrane according to claim 6, characterized in that, the structural resin: the first solvent: the second solvent is (0.5g to 2.0g): (5.0ml to 9.0ml): ( 1.0ml to 5.0ml).
The porous fiber composite membrane according to claim 6, wherein the functional resin: the third solvent: the fourth solvent is (0.5g to 2.0g): (5.0ml to 9.0ml): ( 1.0ml to 5.0ml).
The porous fiber composite membrane according to claim 3, wherein the preparation method further comprises:

Heat treatment step: collecting the porous fiber composite diaphragm from the substrate and placing it on a substrate, and heat treating the porous fiber composite diaphragm at a temperature.
The manufacturing method according to claim 12, wherein the substrate comprises a glass plate.
The preparation method according to claim 12, wherein the temperature is between 100°C and 150°C.