Lithium ion battery composite diaphragm and preparation method thereof

Abstract

The invention provides a lithium ion battery composite diaphragm and a preparation method thereof, the lithium ion battery composite diaphragm comprises a polyolefin base membrane and a coating slurry layer coated on at least one surface of the polyolefin base membrane, the coating slurry layer comprises oxidized fiber pulp and halloysite nanotubes, the oxidized fiber pulp is prepared from fiber pulp and an oxidizing agent. According to the invention, through the coating slurry containing oxidized fiber pulp and halloysite nanotubes, the adsorption capacity of the composite diaphragm to an electrolyte is remarkably enhanced, so that the internal resistance of a battery is reduced, the migration coefficient of lithium ions is improved, the charge-discharge efficiency and rate capability of the battery are improved, and the composite diaphragm has a relatively high practical value.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery diaphragms, and in particular to a lithium ion battery composite diaphragm and a preparation method thereof. Background Art

[0002] Lithium-ion batteries (LIBs) are composed of four main parts, including the positive electrode, the negative electrode, the electrolyte, and the separator. The separator does not directly participate in the reaction, but it plays a vital role in the composition of the battery. It can effectively prevent the positive and negative electrodes from contacting each other, thereby avoiding short circuits in the battery. In addition, the porous structure allows the separator to store more electrolyte and improve the ion transfer efficiency of the battery. However, the current commercial separators have poor thermal stability, and the increase in temperature can easily cause the separator to shrink, and its wettability is poor. In addition, the growth of lithium dendrites cannot be effectively suppressed during the cycle process, which increases the risk of puncturing the separator, easily causing battery short circuits, and causing safety accidents. Summary of the invention

[0003] In view of the above-mentioned deficiencies of the prior art, the present invention provides a lithium-ion battery composite diaphragm and a preparation method thereof. Oxidized fiber pulp and halloysite nanotubes are combined to form a slurry, which is coated on a base film to obtain a lithium-ion battery composite diaphragm, so as to solve the problems of low liquid absorption rate, small lithium ion migration coefficient and difficulty in effectively inhibiting lithium dendrite growth existing in the existing polyolefin base film.

[0004] The technical solution provided by the present invention is: a lithium-ion battery composite separator, comprising a polyolefin base film and a coating slurry layer coated on at least one surface of the polyolefin base film, wherein the coating slurry layer comprises oxidized fiber pulp and halloysite nanotubes, and the oxidized fiber pulp is prepared from fiber pulp and an oxidant.

[0005] Furthermore, the mass fraction of the halloysite nanotubes in the coating slurry is 10-30%, and the mass ratio of the oxidized fiber pulp to the halloysite nanotubes is 1:4-10.

[0006] Furthermore, the fiber pulp is any one of lignin, aramid, PPS, PI, PEEK, and PVDF, the particle size of the fiber pulp is between 0.2-20 um, and the average fiber length is 0.5-5 mm.

[0007] Furthermore, the oxidant is any one of hydrogen peroxide, peracetic acid, potassium permanganate, and potassium dichromate.

[0008] Furthermore, the coating slurry layer has a thickness of 1-50 um.

[0009] Furthermore, the polyolefin-based film is any one of PP, PE, and PP / PE composite film, and the thickness of the polyolefin-based film is 3-100 um.

[0010] Another technical solution provided by the present invention is a method for preparing a composite separator for a lithium-ion battery, comprising the following steps:

[0011] (1) placing fiber pulp in a solution containing an oxidant and reacting it at a temperature of 20-80° C. for 1-10 hours, wherein the mass concentration of the oxidant is 1%-20%, and filtering, washing, neutralizing and drying after the reaction to obtain oxidized fiber pulp;

[0012] (2) dispersing the halloysite nanotubes in water and subjecting the water to ultrasonic treatment for 10-60 minutes to obtain a uniformly dispersed halloysite nanotube solution;

[0013] (3) mixing the oxidized fiber pulp with the halloysite nanotube solution, adding a binder and a wetting agent, and stirring for 30-180 minutes to obtain a coating slurry;

[0014] (4) The coating slurry is coated on the polyolefin base film by dipping, spraying or blade coating, and then dried at 50-150° C. for 5-60 min to obtain a lithium ion battery composite separator.

[0015] Furthermore, in step (1), the mass ratio of the fiber pulp to the oxidant solution is 1:2-1:4.

[0016] Furthermore, the binder is at least one of LA133 binder, LA132 binder, acrylonitrile binder, acrylic resin binder, and polyvinyl pyrrolidone, and the mass fraction of the binder in the coating slurry is 1%-5%.

[0017] Furthermore, the wetting agent is selected from one or more of polyoxyethylene ethyl ether, propylene glycol, glycerol, polyethylene glycol ether, and stearyl alcohol, and the mass fraction of the wetting agent in the coating slurry is 0.1-5%.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention provides a lithium-ion battery composite diaphragm and a preparation method thereof, wherein a coating slurry is composed of oxidized fiber pulp and halloysite nanotubes in a certain ratio, the carboxyl groups in the oxidized fiber pulp and the hydroxyl groups in the halloysite nanotubes have a strong affinity for the electrolyte, which significantly enhances the adsorption capacity of the composite diaphragm for the electrolyte, thereby reducing the internal resistance of the battery and improving the migration coefficient of lithium ions.

[0020] In addition, the synergistic effect of the two makes the prepared composite separator have higher lithium ion migration characteristics, which can improve the battery's charge and discharge efficiency and rate performance. In addition, halloysite nanotubes effectively prevent the penetration of lithium dendrites through the dual mechanisms of physical blocking and chemical adsorption, greatly reducing the risk of short circuits inside the battery, providing double protection for the cycle performance and safety of lithium-ion batteries. DETAILED DESCRIPTION

[0021] In order to make the objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below in conjunction with specific embodiments.

[0022] Example 1

[0023] A method for preparing a lithium-ion battery composite diaphragm comprises the following steps:

[0024] Step 1: placing lignin pulp in a hydrogen peroxide solution with a mass concentration of 5%, wherein the mass ratio of lignin pulp to 5% hydrogen peroxide solution is 1:3; reacting at 60° C. for 1 hour, filtering, washing, neutralizing and drying after the reaction to obtain oxidized lignin pulp;

[0025] Step 2: dispersing the halloysite nanotubes in water and subjecting the water to ultrasonic treatment for 30 minutes to obtain a uniformly dispersed halloysite nanotube solution;

[0026] Step 3: mixing the oxidized lignin pulp and the halloysite nanotube solution in a mass ratio of 1:5, adding a binder LA133 and a wetting agent propylene glycol, and stirring for 60 minutes to obtain a coating slurry, wherein the mass fraction of the halloysite nanotubes in the coating slurry is 16%, the mass fraction of the binder LA133 is 3%, and the mass fraction of the wetting agent propylene glycol is 1%;

[0027] Step 4: The coating slurry is coated on a polyethylene base film with a thickness of 9 um by a doctor blade coating method, and then dried at 70° C. for 15 minutes to obtain a lithium-ion battery composite separator 1.

[0028] Example 2

[0029] A method for preparing a lithium-ion battery composite diaphragm comprises the following steps:

[0030] Step 1: placing lignin pulp in a peracetic acid solution with a mass concentration of 8%, wherein the mass ratio of lignin pulp to the 8% peracetic acid solution is 1:2; reacting at a temperature of 50° C. for 1 hour, filtering, washing, neutralizing, and drying after the reaction to obtain oxidized lignin pulp;

[0031] Step 2: dispersing the halloysite nanotubes in water and subjecting the water to ultrasonic treatment for 20 minutes to obtain a uniformly dispersed halloysite nanotube solution;

[0032] Step 3: mixing the oxidized lignin pulp and the halloysite nanotubes in a mass ratio of 1:4, adding an acrylonitrile binder and a wetting agent glycerol, and stirring for 40 minutes to obtain a coating slurry, wherein the mass fraction of the halloysite nanotubes in the coating slurry is 15%, the mass fraction of the acrylonitrile binder is 3.5%, and the mass fraction of the wetting agent glycerol is 1.2%;

[0033] Step 4: The coating slurry is coated on a polypropylene base film with a thickness of 12 um by a doctor blade coating method, and then dried at 75° C. for 10 min to obtain a lithium-ion battery composite separator 2.

[0034] Example 3

[0035] Step 1: placing aramid pulp in a 10% potassium permanganate solution, wherein the mass ratio of aramid pulp to the 10% potassium permanganate solution is 1:3, reacting at 80° C. for 1.5 hours, filtering, washing, neutralizing and drying after the reaction to obtain oxidized aramid pulp;

[0036] Step 2: dispersing the halloysite nanotubes in water and subjecting the water to ultrasonic treatment for 30 minutes to obtain a uniformly dispersed halloysite nanotube solution;

[0037] Step 3: mixing oxidized aramid pulp and halloysite nanotubes in a mass ratio of 3:20, adding a binder LA132 and a wetting agent polyethylene glycol ether, and stirring for 60 minutes to obtain a coating slurry, wherein the mass fraction of the halloysite nanotubes in the coating slurry is 17%, the mass fraction of the binder LA132 is 3%, and the mass fraction of the wetting agent polyethylene glycol ether is 1.5%;

[0038] Step 4: The coating slurry is coated on a polyethylene base film with a thickness of 9 um by a doctor blade coating method, and then dried at 80° C. for 10 min to obtain a lithium ion battery composite separator 3.

[0039] Example 4

[0040] Step 1: placing aramid pulp in a 10% potassium dichromate solution, wherein the mass ratio of aramid pulp to 8% potassium dichromate solution is 1:3; reacting at 80° C. for 2 hours, filtering, washing, neutralizing and drying after the reaction to obtain oxidized aramid pulp;

[0041] Step 2: dispersing the halloysite nanotubes in water and subjecting the water to ultrasonic treatment for 25 minutes to obtain a uniformly dispersed halloysite nanotube solution;

[0042] Step 3: mixing oxidized aramid pulp and halloysite nanotubes in a mass ratio of 2:9, adding a binder LA133 and a wetting agent glycerol, and stirring for 60 minutes to obtain a coating slurry, wherein the mass fraction of the halloysite nanotubes in the coating slurry is 15%, the mass fraction of the binder LA133 is 4%, and the mass fraction of the wetting agent glycerol is 1%;

[0043] Step 4: The coating slurry is coated on a polypropylene base film with a thickness of 12 μm by blade coating, and then dried at 78° C. for 15 min to obtain a lithium ion battery composite separator 4. Comparative Example 1:

[0044] A lithium-ion battery composite diaphragm, the specific embodiment of which is the same as that of embodiment 1, except that the main component of the coating slurry is oxidized lignin pulp.

[0045] Comparative Example 2:

[0046] A lithium-ion battery composite diaphragm, the specific embodiment of which is the same as that of embodiment 1, except that the main component of the coating slurry is halloysite nanotubes.

[0047] Comparative Example 3:

[0048] 9umPE base film

[0049] Performance Testing:

[0050] 1) The contact angle test of the membranes obtained in the embodiments of the present invention and the comparative examples was performed as follows:

[0051] Contact angle test: The diaphragm was cut into 5 cm × 5 cm squares and a contact angle tester was used to perform a dynamic contact angle test. The acquisition interval was 10,000 milliseconds per frame, and 10 sets of data were tested. The test results are shown in Table 1.

[0052] Table 1 Contact angle test data

[0053]

[0054] It can be seen from the above test results that the lithium-ion battery composite diaphragm prepared by the present invention is superior to other comparison cases in terms of wettability, significantly enhancing the adsorption capacity of the composite diaphragm to the electrolyte, thereby reducing the internal resistance of the battery, increasing the migration coefficient of lithium ions, and being able to improve the battery's charge and discharge efficiency and rate performance.

[0055] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium-ion battery composite diaphragm, characterized in that: The invention comprises a polyolefin-based film and a coating slurry layer coated on at least one surface of the polyolefin-based film. The coating slurry layer comprises oxidized fiber pulp and halloysite nanotubes. The oxidized fiber pulp is prepared from fiber pulp and an oxidant.

2. A lithium-ion battery composite separator according to claim 1, characterized in that: The mass fraction of the halloysite nanotubes in the coating slurry is 10-30%, and the mass ratio of the oxidized fiber pulp to the halloysite nanotubes is 1:4-10.

3. A lithium-ion battery composite separator according to claim 1, characterized in that: The fiber pulp is any one of lignin, aramid, PPS, PI, PEEK, and PVDF. The particle size of the fiber pulp is between 0.2-20um, and the average fiber length is 0.5-5mm.

4. A lithium-ion battery composite separator according to claim 1, characterized in that: The oxidant is any one of hydrogen peroxide, peracetic acid, potassium permanganate and potassium dichromate.

5. A lithium-ion battery composite separator according to claim 1, characterized in that: The thickness of the coating slurry layer is 1-50 um.

6. A lithium-ion battery composite separator according to claim 1, characterized in that: The polyolefin-based film is any one of PP, PE, and PP / PE composite films, and the thickness of the polyolefin-based film is 3-100 um.

7. The method for preparing a lithium ion battery composite diaphragm according to any one of claims 1 to 6, characterized in that: The steps include: (1) placing fiber pulp in a solution containing an oxidant and reacting it at a temperature of 20-80° C. for 1-10 hours, wherein the mass concentration of the oxidant is 1%-20%, and filtering, washing, neutralizing and drying after the reaction to obtain oxidized fiber pulp; (2) dispersing the halloysite nanotubes in water and subjecting the water to ultrasonic treatment for 10-60 minutes to obtain a uniformly dispersed halloysite nanotube solution; (3) mixing the oxidized fiber pulp with the halloysite nanotube solution, adding a binder and a wetting agent, and stirring for 30-180 minutes to obtain a coating slurry; (4) The coating slurry is coated on the polyolefin base film by dipping, spraying or blade coating, and then dried at 50-150° C. for 5-60 min to obtain a lithium ion battery composite separator.

8. The method for preparing a lithium ion battery composite diaphragm according to claim 7, characterized in that: In the step (1), the mass ratio of fiber pulp to oxidant solution is 1:2-4.

9. The method for preparing a lithium ion battery composite diaphragm according to claim 7, characterized in that: The binder is at least one of LA133 binder, LA132 binder, acrylonitrile binder, acrylic resin binder and polyvinyl pyrrolidone, and the mass fraction of the binder in the coating slurry is 1%-5%.

10. The method for preparing a lithium ion battery composite diaphragm according to claim 7, characterized in that: The wetting agent is selected from one or more of polyoxyethylene ethyl ether, propylene glycol, glycerol, polyethylene glycol ether, and stearyl alcohol, and the mass fraction of the wetting agent in the coating slurry is 0.1-5%.

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