PPSSO fiber-based lithium battery composite diaphragm and preparation method thereof

Abstract

The invention discloses a PPSSO fiber-based lithium battery composite diaphragm and a preparation method thereof. According to the method, PPSSO chopped fibers and different fiber pulps are used as raw materials, the PPSSO chopped fibers and the pulps are dissociated and dispersed, a wet papermaking process is adopted for sheet making and forming, diaphragm body paper is treated through a hot pressing process, the PPSSO fiber-based lithium battery composite diaphragm is prepared, the composite diaphragm is modified through a solution grafting method, and the composite diaphragm is prepared. The mechanical property and the electrochemical property of the composite diaphragm are enhanced. The preparation method of the PPSSO fiber-based lithium battery composite diaphragm provided by the invention is simple, and the prepared PPSSO fiber-based lithium battery composite diaphragm has the characteristics of high temperature resistance, flame retardance, corrosion resistance, wettability, excellent stability and the like. The lithium ion battery has a wide application prospect in lithium battery products, and the safety performance, the rate capability and the cycle performance of the lithium battery can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery materials, and particularly relates to a PPSSO fiber-based lithium battery composite separator and a preparation method thereof. Background Art

[0002] As one of the key component materials of lithium-ion batteries, the main function of the separator is to isolate the positive and negative electrodes of the battery to prevent direct contact between the two poles and short circuit. The performance of the separator will directly affect the performance of lithium-ion batteries. Therefore, choosing a suitable separator material is crucial in the manufacture of lithium batteries. At present, the most widely used separators in lithium-ion batteries are mainly polyolefin microporous membranes, such as polyethylene (PE) separators, polypropylene (PP) separators, single-layer or multi-layer composite membranes. The production process is relatively mature, and the mechanical strength and electrochemical stability are excellent. However, due to the low melting point of its raw materials, when the battery operates with local abnormal heating, the separator will be deformed, shrunk and melted by heat, resulting in internal short circuit of the battery, and even accidents such as fire and explosion. At the same time, in some special scenarios, glass fiber separators are used to solve the problem of high temperature resistance of the separator, but its mechanical properties are poor, and the tensile strength is less than 1 MPa. During the assembly and winding process of large batteries, it is easy to damage the separator, posing a safety hazard. In addition, its relatively high price also limits its further use. In recent years, with the increasing requirements for battery performance, the attention to the safety performance of separators has also increased. At present, the problems that need to be solved are the easy shrinkage of polyolefin microporous membranes by heat and the insufficient tensile strength of glass fiber separators. Therefore, it is of great significance to develop lithium-ion battery separators with high safety and high stability.

[0003] Polyphenylsulfone sulfoxide fiber (PPSSO) is an innovative variety of high-performance fibers. It can be used for a long time at temperatures above 260 °C, and the limiting oxygen index is 36%. It can be quickly extinguished after combustion and has excellent self-extinguishing performance. Compared with polyimide fibers, aramid fibers, and polyphenylene sulfide fibers, it has more excellent thermal stability, chemical resistance, and antioxidant properties. The uses of PPSSO fibers are very extensive. At present, it has been successfully applied in filtration and separation materials and is one of the organic high-performance fibers with the highest use temperature in current filtration and separation materials. Based on its excellent high temperature resistance, acid and alkali resistance, hydrolysis resistance, and antioxidant properties, it has a huge application market in industries such as fiber membranes, special papers, thermal protection, and chemical protection. Summary of the Invention

[0004] To solve the problems of poor high temperature resistance, flame retardancy of traditional polyolefin separators and insufficient tensile strength of glass fiber separators, the present invention provides a PPSSO fiber-based lithium battery composite separator and a preparation method thereof. Using PPSSO fibers as the framework, it is compounded with a variety of pulp to prepare a lithium-ion battery separator with excellent thermal stability, chemical stability, and high porosity, and the solution grafting method is used to enhance the mechanical properties and electrochemical properties of the composite separator.

[0005] The present invention provides a method for preparing a PPSSO fiber-based lithium battery composite separator, comprising the following steps: (1) Dispersing PPSSO short-cut fibers and fiber pulp in water, and adding a dispersant to fully dissociate them to obtain a suspension of PPSSO short-cut fibers and fiber pulp.

[0006] (2) Forming the suspension of PPSSO short-cut fibers and fiber pulp prepared in (1) into a sheet by a wet papermaking process, and then drying to obtain a PPSSO composite separator base paper.

[0007] (3) Thermally pressing the PPSSO composite separator base paper prepared in (2) by a hot pressing process to obtain a PPSSO fiber-based lithium battery composite separator.

[0008] (4) Grafting and modifying the PPSSO fiber-based lithium battery composite separator prepared in (3) with an organic-inorganic composite solution to obtain an inorganic particle-modified PPSSO fiber-based lithium ion battery composite separator.

[0009] In the step (1), the diameter of the PPSSO short-cut fibers is 1-25 μm, and the length is 3-15 mm.

[0010] In the step (1), the fiber pulp is one or more of polyphenylsulfone sulfoxide, para-aramid, meta-aramid, cellulose fiber, arylsulfone aramid, and polyimide fiber pulp.

[0011] In the step (1), the absolute dry mass ratio of the PPSSO short-cut fibers to the fiber pulp is (30-80):(70-20), preferably, the absolute dry mass ratio of the PPSSO short-cut fibers to the fiber pulp is (40-60):(60-40).

[0012] In the step (1), the dispersant is one or more of potassium pyrophosphate, sodium hexametaphosphate, and sodium tetraphosphate.

[0013] In the step (1), the addition amount of the dispersant is 0.1%-2% of the mass of the mixed fibers (PPSSO short-cut fibers + fiber pulp), preferably, the addition amount of the dispersant is 0.5%-1% of the mass of the mixed fibers.

[0014] In the step (1), the preparation method of the suspension of PPSSO fibers and fiber pulp is to add PPSSO short-cut fibers and fiber pulp to a fiber defibrator, add a dispersant, and the defibrating speed is 1000-5000 rpm, and the defibrating revolution number is 15000-30000 r, preferably, the defibrating speed is 3000 rpm.

[0015] In step (1), the concentration of the PPSSO short-cut fiber / fiber pulp suspension slurry is 0.5 wt% - 2.2 wt%, preferably, the concentration of the suspension slurry is 1 wt%.

[0016] In step (2), the drying temperature is 80 - 120 °C, and the drying time is 3 - 10 min. Preferably, the drying temperature is 100 °C, and the drying time is 5 min.

[0017] In step (3), the hot pressing temperature is 160 - 280 °C, the hot pressing pressure is 5 - 25 MPa, and the hot pressing time is 0.5 - 15 min. Preferably, the hot pressing temperature is 200 - 240 °C, the hot pressing pressure is 10 - 15 MPa, and the hot pressing time is 6 - 10 min.

[0018] In step (4), the grafting time of the organic-inorganic composite solution is 30 - 120 min. Preferably, the grafting time of the organic-inorganic composite solution is 60 - 90 min.

[0019] In step (4), the organic-inorganic composite solution is prepared by self-assembly of an organic solvent, deionized water, and inorganic particles through a binder.

[0020] The inorganic particles are one or more of boehmite, alumina, hydroxyapatite, and titanium dioxide.

[0021] The average particle size of the inorganic particles is 0.1 - 2 μm.

[0022] In the organic-inorganic composite solution, the mass fraction of the inorganic particles is 1% - 10%. Preferably, the mass fraction of the inorganic particles is 6% - 10%.

[0023] The organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0024] The organic binder is one or more of polyvinyl alcohol, polyvinyl alcohol ether, polyacrylic acid, and chitosan.

[0025] In the organic-inorganic composite solution, the mass fraction of the organic binder is 2 - 20 wt.%. Preferably, the mass fraction of the organic binder is 5 - 15 wt.%.

[0026] The present invention has the following advantages: (1) The PPSSO fiber-based lithium battery composite separator prepared by the papermaking method provided by the present invention has the advantages of simple process, low cost, and a wide range of optional materials.

[0027] (2)The PPSSO fiber-based lithium battery composite separator prepared by the present invention has excellent high temperature resistance, flame retardancy, corrosion resistance, wettability and stability, and has broad application prospects in the new generation of lithium batteries.

[0028] (3)Introducing an organic-inorganic composite solution as the grafting solution to graft inorganic particles onto the surface of the composite separator can enhance the mechanical strength of the composite separator while reducing the impact on the hydrophilicity of the composite separator. Inorganic materials such as boehmite and hydroxyapatite optimize the interfacial compatibility between the separator and the electrode, improve the electrochemical performance of the separator and the performance of the battery assembled using it, and ensure the long-term stable operation of the battery. Description of the Drawings

[0029] Figure 1 It is the preparation flow chart of the boehmite-modified PPSSO fiber-based lithium battery composite separator in Example 2 of the present invention.

[0030] Figure 2 It is the scanning electron micrograph of the boehmite-modified PPSSO fiber-based lithium battery composite separator in Example 2 of the present invention.

[0031] Figure 3 It is the thermogravimetric curve of the boehmite-modified PPSSO fiber-based lithium battery composite separator in Example 2 of the present invention.

[0032] Figure 4 It is the wetting angle image of the boehmite-modified PPSSO fiber-based lithium battery composite separator in Example 2 of the present invention.

[0033] Figure 5 It is the combustion schematic diagram of the boehmite-modified PPSSO fiber-based lithium battery composite separator in Example 2 of the present invention. Detailed Embodiments

[0034] The technical solutions of the present invention will be described in detail below through examples. The following examples are only exemplary and can only be used to explain and illustrate the technical solutions of the present invention, and cannot be construed as a limitation to the technical solutions of the present invention.

[0035] As Figure 1 shown, the preparation method of the PPSSO fiber-based lithium battery composite separator provided by the embodiment of the present invention includes: S1, preparation of the PPSSO fiber and pulp suspension; S2, forming the PPSSO composite separator base paper by papermaking; S3, drying the PPSSO composite separator base paper; S4, hot pressing the PPSSO composite separator into shape; S5, grafting modification of the PPSSO composite separator.

[0036] The present invention will be further described below in conjunction with specific embodiments.

[0037] Example 1 A preparation method of a PPSSO fiber-based lithium battery composite separator is as follows: Disperse 40 parts by weight of PPSSO short-cut fibers and 60 parts by weight of meta-aramid pulp in 1000 parts by weight of water, and add 1 part by weight of dispersant potassium pyrophosphate to make it fully dissociated (refining speed 3000 rpm, refining revolution 20000 r) to obtain a suspension of PPSSO fibers and meta-aramid pulp. Form the suspension into a sheet by wet papermaking process, and vacuum dry it at 100 °C for 5 min to obtain the PPSSO composite separator base paper. Use the hot pressing process to perform a 6-min hot pressing treatment on the PPSSO composite separator base paper at 200 °C and 10 MPa to obtain the PPSSO fiber-based lithium battery composite separator. After testing, the thickness of the PPSSO fiber-based lithium battery composite separator prepared in Example 1 is 65 μm, the maximum pore diameter is 3.88 μm, the average pore diameter is 0.30 μm, the porosity is 64.1%, the liquid absorption rate is 238%, the wetting angle is 60 °, and the ultimate tensile strength is 5.94 MPa.

[0038] Example 2 A preparation method of a PPSSO fiber-based lithium battery composite separator is as follows: Disperse 50 parts by weight of PPSSO short fibers, 40 parts by weight of meta-aramid pulp, and 10 parts by weight of cellulose fiber pulp in 1000 parts by weight of water, and add 1 part by weight of the dispersant potassium pyrophosphate to fully dissociate them (refining speed 3000 rpm, refining revolution 20000 r) to obtain a suspension of PPSSO fibers, meta-aramid pulp, and cellulose fiber pulp. Form a sheet by wet papermaking process for the suspension, and vacuum dry it at 100 °C for 5 min to obtain the PPSSO composite separator base paper. Use the hot pressing process to perform a 6-min hot pressing treatment on the PPSSO composite separator base paper at 200 °C and 10 MPa to obtain the PPSSO fiber-based lithium battery composite separator. Add 6 parts by weight of N,N-dimethylformamide, 6 parts by weight of boehmite, 4 parts by weight of polyvinyl alcohol, 6 parts by weight of chitosan, and 78 parts by weight of deionized water into a beaker, stir magnetically for 30 minutes, and ultrasonically disperse for 30 minutes to uniformly mix the solution. Immerse the PPSSO composite separator into the grafting solution for 1 h, wash the reacted PPSSO composite separator 3 times with warm water at 60 °C, and then dry it in an oven at 100 °C for 2 h to obtain the boehmite-modified PPSSO fiber-based lithium battery composite separator. After testing, the thickness of the boehmite-modified polyphenylsulfone sulfoxide fiber-based lithium battery composite separator prepared in Example 2 is 70 μm, the maximum pore diameter is 1.65 μm, the average pore diameter is 0.35 μm, the porosity is 70.9%, the liquid absorption rate is 229%, the wetting angle is 51 °, and the ultimate tensile strength is 9.59 MPa.

[0039] Example 3 A preparation method of a PPSSO fiber-based lithium battery composite separator, the specific steps are as follows: Disperse 50 parts by weight of PPSSO short fibers, 40 parts by weight of meta-aramid pulp, and 10 parts by weight of cellulose fiber pulp in 1000 parts of water, and add 1 part by weight of dispersant potassium pyrophosphate to fully dissociate them (refining speed 3000 rpm, refining revolution 20000 r) to obtain a suspension of PPSSO fibers, meta-aramid pulp, and cellulose fiber pulp. Form the suspension into a sheet by wet papermaking process, and vacuum dry it at 100 °C for 5 min to obtain the PPSSO composite separator base paper. Use the hot pressing process to perform a 6-min hot pressing treatment on the PPSSO composite separator base paper at 200 °C and 10 MPa to obtain the PPSSO fiber-based lithium battery composite separator. Add 6 parts by weight of N,N-dimethylacetamide, 8 parts by weight of hydroxyapatite, 6 parts by weight of polyvinyl alcohol, 4 parts by weight of chitosan, and 76 parts by weight of deionized water into a beaker, stir magnetically for 30 minutes, and ultrasonically disperse for 30 minutes to make the solution uniformly mixed. Immerse the PPSSO composite separator into the grafting solution for 1 h, wash the reacted PPSSO composite separator 3 times with warm water at 60 °C, and then dry it in an oven at 100 °C for 2 h to obtain the hydroxyapatite-modified PPSSO fiber-based lithium battery composite separator. After testing, the thickness of the hydroxyapatite-modified polyphenylsulfone sulfoxide fiber-based lithium battery composite separator prepared in Example 3 is 70 μm, the maximum pore size is 1.25 μm, the average pore size is 0.41 μm, the porosity is 71.3%, the liquid absorption rate is 239%, the wetting angle is 49 °, and the ultimate tensile strength is 9.22 MPa.

[0040] The performance comparisons of the PP separator, the PPSSO fiber-based lithium battery composite separator obtained in Example 1, and the inorganic particle-modified PPSSO fiber-based lithium battery composite separators obtained in Example 2 and Example 3 are shown in the following table: From the data in the above table, it can be seen that the PPSSO fiber-based lithium battery composite separator prepared by the preparation methods described in Examples 1-3 of the present invention has excellent thermal dimensional stability compared with the PP separator. From the data comparison of Examples 1, 2, 3 and the PP separator, the ionic conductivity, electrochemical stability window, and long cycle performance of the PPSSO fiber-based lithium battery composite separator are more excellent than those of the PP separator, and the ionic conductivity and long cycle performance of the composite separator after grafting modification are further enhanced.

[0041] From Figure 2 It can be seen that the inorganic particles on the surface of the PPSSO fiber-based lithium battery composite separator prepared by the preparation method of the present invention are uniformly dispersed after grafting modification.

[0042] From Figure 3It can be seen that the PPSSO fiber-based lithium battery composite separator prepared by the preparation method of the present invention has more excellent thermal stability than the PP separator.

[0043] From Figure 4 It can be seen that the PPSSO fiber-based lithium battery composite separator prepared by the preparation method of the present invention has good affinity for the electrolyte.

[0044] From Figure 5 It can be seen that the PPSSO fiber-based lithium battery composite separator prepared by the preparation method of the present invention has excellent flame retardant performance.

[0045] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A preparation method of a PPSSO fiber-based lithium battery composite separator, characterized in that, It includes the following preparation steps: Disperse the chopped polyphenylsulfone sulfoxide (PPSSO) fibers and fiber pulp in water, and add a dispersant to fully dissociate them to obtain a suspension of chopped PPSSO fibers and fiber pulp; form a sheet by the wet papermaking process for the suspension, dry it to obtain the PPSSO separator base paper, and then perform hot pressing treatment on the PPSSO separator base paper by the hot pressing process to prepare a PPSSO fiber-based lithium battery composite separator; graft-modify the PPSSSO composite separator with an organic-inorganic composite solution to obtain an inorganic particle-modified PPSSO fiber-based lithium ion battery composite separator.

2. The preparation method of the PPSSO fiber-based lithium battery composite separator according to claim 1, wherein, The diameter of the chopped PPSSO fibers is 1 - 25 μm, and the length is 3 - 15 mm.

3. The preparation method of the PPSSO fiber-based lithium battery composite separator according to claim 1, characterized in that, The fiber pulp is one or more of polyphenylsulfone sulfoxide, polyphenylene sulfide, para-aramid, meta-aramid, cellulose fiber, arylsulfone aramid, polyimide fiber pulp; the absolute dry mass ratio of chopped PPSSO fibers to fiber pulp is (30 - 80):(70 - 20); the concentration of the suspension slurry of chopped PPSSO fibers and fiber pulp is 0.5 wt% - 2.2 wt%.

4. The preparation method of the PPSSO fiber-based lithium battery composite separator according to claim 1, characterized in that, The defibration speed during the dissociation process of chopped PPSSO fibers and fiber pulp is 1000 - 5000 rpm, and the defibration revolution is 15000 - 30000 r.

5. The preparation method of the PPSSO fiber-based lithium battery composite separator according to claim 1, characterized in that, The dispersant includes one or more of potassium pyrophosphate, sodium hexametaphosphate, and sodium tetraphosphate; the addition amount of the dispersant is 0.1% - 2% of the total mass of chopped PPSSO fibers and fiber pulp.

6. The preparation method of the PPSSO fiber-based lithium battery composite separator according to claim 1, characterized in that, In the preparation steps, the drying temperature is 80 - 120 °C, and the drying time is 3 - 10 min; the hot pressing temperature is 160 - 280 °C, the hot pressing pressure is 5 - 25 MPa, and the hot pressing time is 0.5 - 15 min.

7. The preparation method of the PPSSO fiber-based lithium battery composite separator according to claim 1, wherein, In the preparation steps, the grafting time of the organic-inorganic composite solution is 30 - 120 min; the organic-inorganic composite solution is prepared by self-assembly of an organic solvent, deionized water, and inorganic particles through an organic binder.

8. The preparation method of the PPSSO fiber-based lithium battery composite separator according to claim 7, characterized in that, The inorganic particles are one or more of boehmite, alumina, hydroxyapatite, and titanium dioxide; the average particle size of the inorganic particles is 0.1 - 2 μm; the mass fraction of the inorganic particles in the organic-inorganic composite solution is 1% - 10%.

9. The preparation method of the PPSSO fiber-based lithium battery composite separator according to claim 7, characterized in that, The organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; the organic binder is one or more of polyvinyl alcohol, polyvinyl alcohol ether, polyacrylic acid, and chitosan; the mass fraction of the organic binder in the organic-inorganic composite solution is 2 - 20%.

10. A PPSSO fiber-based lithium battery composite separator prepared by the preparation method according to any one of claims 1 - 9.

Images