A multiphase composite electrolyte membrane based on ethylenediaminetetraacetic acid and its preparation method

Abstract

The present invention discloses a method for preparing a multiphase composite electrolyte separator based on ethylenediaminetetraacetic acid (EDTA). The method comprises the following steps: a lithium titanium aluminum phosphate (LTA) production process, a LTP particle nano-sizing process, a slurry production process, and a coating, extraction, and drying process. During the above-mentioned preparation process, the introduction of the LTP solid electrolyte significantly improves the ionic conductivity of the gel-state coating; the oxygen on the EDTA coordination bond forms hydrogen bonds with the hydrogen in the aramid, which not only enables the aramid to adsorb metal but also linearizes the aramid structure, resulting in higher temperature resistance; the introduction of the aramid material enhances the separator's bonding strength, heat shrinkage resistance, membrane rupture temperature, and flame retardancy; and the mixing of EDTA into the slurry system effectively blocks the metal oxidation process at the positive electrode and then reduction at the negative electrode, preventing the formation of hard metal edges that pierce the separator, thereby preventing battery self-discharge.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and in particular to a multiphase composite electrolyte separator based on ethylenediaminetetraacetic acid and a preparation method thereof. Background Art

[0002] While solid-state batteries haven't completely overcome their technical difficulties, high-energy-density power batteries remain a challenge. Safety, charge-discharge efficiency, and self-discharge are all difficult to resolve, and these challenges are often interconnected. For example, while safety can be improved by improving the heat resistance of the diaphragm, the charge-discharge efficiency of heat-resistant diaphragms remains low. This is primarily due to the diaphragm's heat-resistant structure, which is not conducive to improving the battery's charge-discharge efficiency. Regarding self-discharge, the higher the energy density, the greater the battery's self-discharge. This can occur for a variety of reasons, the most prominent of which is the generation of metal ions in the battery. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing a multi-phase composite electrolyte membrane based on ethylenediaminetetraacetic acid in order to address the technical defects in the prior art.

[0004] Another object of the present invention is to provide a multi-phase composite electrolyte membrane based on ethylenediaminetetraacetic acid obtained by the above preparation method.

[0005] The technical solution adopted to achieve the purpose of the present invention is:

[0006] Step 1: Add ethylenediaminetetraacetic acid to dimethylacetamide, stir for 30 to 40 minutes to obtain a mixed solution, ultrasonically treat the mixed solution for 40 to 50 minutes (ultrasonic frequency is 100 to 200 Hz), then add nano-lithium aluminum titanium phosphate powder and ultrasonically treat for 40 to 50 minutes (ultrasonic frequency is 100 to 200 Hz) to obtain an ultrasonically dispersed slurry, and sand-mill the ultrasonically dispersed slurry to obtain a sand-milled slurry; wherein the mass ratio of dimethylacetamide, ethylenediaminetetraacetic acid and lithium aluminum titanium phosphate as raw materials is (55 to 50): (15 to 10): (30 to 40).

[0007] Step 2: adding the sand-milled slurry obtained in step 1 to a device filled with an inert protective gas, adding m-phenylenediamine to the device and stirring for 20 to 50 minutes until dissolved, cooling the device after dissolution, adding isophthaloyl chloride after cooling and stirring for 20 to 50 minutes, then heating and stirring for 30 to 80 minutes, and then adding calcium hydroxide and stirring for 20 to 30 minutes to obtain a mixed slurry from which hydrochloric acid in the reaction is removed; wherein the mass ratio of the sand-milled slurry, m-phenylenediamine, isophthaloyl chloride and calcium hydroxide as raw materials is (88 to 78): (7 to 12): (7 to 12): (5 to 10), and the molar mass ratio of m-phenylenediamine to phthaloyl chloride is 1:1.

[0008] Step 3: Add dimethylacetamide to polyvinylidene fluoride and stir for 60 to 80 minutes to completely dissolve to obtain a mixed solution; wherein the mass ratio of polyvinylidene fluoride and dimethylacetamide as raw materials is (10 to 15): (90 to 85).

[0009] Step 4: adding dimethyl carbonate pore-forming agent to the mixed slurry obtained in step 2 and stirring for 15 to 30 minutes to obtain a mixed solution; wherein the mass ratio of the mixed slurry obtained in step 2 and dimethyl carbonate as raw materials is (95 to 93): (5 to 7).

[0010] Step 5: Mixing and stirring the mixed solution obtained in step 3 and the mixed solution obtained in step 4 for 60 to 80 minutes to obtain a coating slurry; wherein the mass ratio of the mixed solution obtained in step 3 and the mixed solution obtained in step 4 as raw materials is (20 to 30): (80 to 70).

[0011] Step 6: placing the base film on a coating machine equipped with the coating slurry prepared in step 5 for uniform coating, and then pulling it into an extraction tank for extraction, and then pulling it into an oven for drying to obtain a multiphase composite electrolyte membrane;

[0012] In the above technical solution, in step 1, the preparation of the nano-lithium aluminum titanium phosphate powder is to dry ammonium dihydrogen phosphate, lithium carbonate, aluminum oxide and titanium dioxide (temperature 150-200°C), take out and cool, then grind it for the first time to obtain a mixed powder and heat it in a stepwise manner to maintain the temperature, take it out and cool it, crush it and grind it for the second time to obtain the ground powder; wherein, the mass ratio of ammonium dihydrogen phosphate, lithium carbonate, aluminum oxide and titanium dioxide as raw materials is (60-65): (8-10): (2-4): (24-26). The ground powder obtained above is added to ethanol and ball-milled to obtain a mixed solution. After the mixed solution is precipitated for 4 to 6 hours, the floating layer is taken out from the precipitated mixed solution, and dried and ground to obtain nano-lithium aluminum titanium phosphate powder; wherein, the mass ratio of ethanol and lithium aluminum titanium phosphate as raw materials is (60 to 30): (40 to 70); the grinding is carried out using a ball mill, the first grinding speed is 600 to 800 r / min, and the grinding time is 4 to 6 hours; the second grinding speed is 600 to 800 r / min, and the grinding time is 10 to 24 hours; the step-by-step heating and constant temperature is to put the mixed powder into a ceramic crucible and then into a muffle furnace; the step-by-step heating and constant temperature is The temperature is raised to 250-350°C and kept constant for 2 hours, then the temperature is further raised to 450-550°C and kept constant for 2 hours, the temperature is again raised to 650-750°C and kept constant for 2 hours, and finally the temperature is raised to 850-950°C and kept constant for 2 hours, so that the mixed powder releases the reaction gas (such as carbon dioxide and ammonia) evenly, the reaction is more uniform and thorough, and the generation of by-products is reduced; the ball milling adopts a ball mill with an orbital speed of 200-400 r / min, a rotation speed of 600-800 r / min, and a ball milling time of 10-24 hours; the mixed solution after precipitation is divided into three layers, namely, a precipitation layer (particle size of 0.5-2 μm), an intermediate layer (particle size of 200-500 nm) and a floating layer (particle size of 50-100 nm).

[0013] In the above technical solution, in step 1, the sanding is performed using a pin-type sand mill with a sand mill speed of 600 to 800 r / min and a sanding time of 20 to 30 min.

[0014] In the above technical solution, in step 2, the equipment is a reaction tank.

[0015] Preferably, in step 2, the protective gas is nitrogen.

[0016] In the above technical solution, in step 2, the cooling is to introduce cooling water into the equipment and cool it down to 0-5°C, and the heating is to remove the cooling water from the equipment and heat it up to 60-80°C.

[0017] In the above technical solution, in step 6, the base film is a polyethylene base film, and the specification of the polyethylene base film is 800 mm×12 μm.

[0018] In the above technical solution, in step 6, the coating is slit extrusion coating.

[0019] In the above technical solution, in step 6, the traction is carried out by using a traction roller.

[0020] In the above technical solution, in step 6, the extraction tank is an extraction tank with 10 built-in small tanks, each small tank is about 1m deep, and among the small tanks, the first three small tanks in contact with the coated base film extraction are filled with extraction liquid, and the other small tanks are filled with deionized water.

[0021] In the above technical solution, in step 6, the extracting liquid is a solution of deionized water and dimethylacetamide mixed in different content ratios, wherein the ratio of the dimethylacetamide content in the first small groove, the second small groove and the third small groove of the first three small grooves is 60:40:20, and the coated base film passes through the small grooves containing the first, second and third extracting liquids and deionized water in sequence.

[0022] In the above technical solution, in step 6, the drying in the oven adopts two drying methods: hot roller drying and air-heat drying; the hot roller drying has three hot rollers with a diameter of 400 to 600 mm, and the temperature of the hot rollers is set to 80 to 90°C; the temperature of the air-heat drying is set to 50 to 70°C.

[0023] Another aspect of the present invention also includes a multi-phase composite electrolyte membrane obtained by the above preparation method.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The multiphase composite electrolyte membrane of the present invention has a solid-gel composite electrolyte system, whose ionic conductivity is close to that of liquid electrolyte, and thus can be applied to some medium and high power batteries. The introduction of lithium titanium aluminum phosphate solid electrolyte significantly improves the ionic conductivity of the gel coating.

[0026] 2. The oxygen on the coordination bond of EDTA and the hydrogen in aramid (phenylenediamine) form hydrogen bonds, which not only makes aramid capable of adsorbing metals, but also makes the structure of aramid itself linear, so that aramid itself has higher temperature resistance.

[0027] 3. The introduction of aramid material enhances the bonding strength, heat shrinkage resistance, membrane rupture temperature and flame retardancy of the diaphragm. The mixing of ethylenediaminetetraacetic acid into the slurry system can effectively block the process of metal oxidation at the positive electrode and then reduction at the negative electrode, avoiding the formation of hard metal edges that pierce the diaphragm, thereby avoiding battery self-discharge.

[0028] 4. Raw materials such as lithium titanium aluminum phosphate, polyvinylidene fluoride, ethylenediaminetetraacetic acid, and aramid are mixed through a special ratio process to form a stable slurry. The main organic matter in the slurry is dissolved in a polar solvent, forming a homogeneous solution with a certain viscosity. Nano-scale lithium titanium aluminum phosphate is suspended in it, forming a stable and uniform dispersion system with electrostatic balance. Polyvinylidene fluoride can gel the electrolyte in the battery system and provide adhesion to the electrodes. The introduction of lithium titanium aluminum phosphate solid electrolyte significantly improves the ionic conductivity of the gel coating. The introduction of aramid material enhances the adhesion strength, heat shrinkage resistance, membrane rupture temperature, and flame retardancy of the separator. The addition of ethylenediaminetetraacetic acid into the slurry system can effectively prevent gold from oxidizing at the positive electrode and then reducing at the negative electrode, forming hard metal edges that pierce the separator and cause battery self-discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Shown is a scanning electron microscope image of the surface of the multiphase composite electrolyte membrane prepared in Example 1 of the present invention.

[0030] Figure 2 Shown is the preparation flow chart of step 6 of the technical solution of the present invention.

[0031] Figure 3 Shown is the linear structure aramid synthesis reaction formula of step 2 of the technical solution of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0033] Example 1

[0034] A method for preparing a multiphase composite electrolyte membrane based on ethylenediaminetetraacetic acid comprises the following steps:

[0035] Step A, drying ammonium dihydrogen phosphate, lithium carbonate, aluminum oxide and titanium dioxide (temperature 150°C), taking out and cooling, and then using a ball mill for the first grinding (grinding speed of 500r / min, grinding time of 4h) to obtain a mixed powder, placing the mixed powder into a ceramic crucible, and then placing it into a muffle furnace for step-by-step heating and constant temperature (heating to 250°C, constant temperature for 2h, then continuing to heat to 450°C, constant temperature for 2h, heating again to 650°C, constant temperature for 2h, and finally heating to 850°C, constant temperature for 2h), taking out and cooling, crushing and performing a second grinding (grinding speed of 600r / min, grinding time for 10h) to obtain a ground powder; wherein, the mass ratio of ammonium dihydrogen phosphate, lithium carbonate, aluminum oxide and titanium dioxide as raw materials is 60:8:2:24.

[0036] In step A, the ammonium dihydrogen phosphate, lithium carbonate, aluminum oxide and titanium dioxide are calcined together at high temperature. In the molten state, titanium, lithium and aluminum are strongly adsorbed together by phosphorus, and the bond positions of titanium, lithium and aluminum are almost exposed.

[0037] In step A, the stepwise heating allows the mixed powder to evenly release reaction gases (such as carbon dioxide and ammonia), making the reaction more uniform and thorough and reducing the generation of by-products.

[0038] Step B, adding the ground powder obtained in step A to ethanol, using a ball mill for ball milling (revolution speed of 200r / min, rotation speed of 600r / min, ball milling time of 10h) to obtain a mixed solution, and precipitating the mixed solution for 24h to obtain a precipitated mixed solution, wherein the precipitated mixed solution is divided into three layers, namely a precipitation layer (particle size of 0.5-2μm), an intermediate layer (particle size of 200-500nm) and a floating layer (particle size of 50-100nm), and the floating layer is taken out from the precipitated mixed solution, dried and ground to obtain nano-lithium aluminum titanium phosphate powder; wherein the mass ratio of ethanol and lithium aluminum titanium phosphate as raw materials is 60:40.

[0039] Step 1: Add ethylenediaminetetraacetic acid to dimethylacetamide, stir for 30 to 40 minutes to obtain a mixed solution, ultrasonicate the mixed solution for 40 to 50 minutes (ultrasonic frequency of 100 Hz), then add nano-lithium aluminum titanium phosphate powder and ultrasonicate for 40 to 50 minutes (ultrasonic frequency of 100 Hz) to obtain an ultrasonically dispersed slurry, and sand-mill the ultrasonically dispersed slurry using a pin-type sand mill (speed of 600 r / min, sand-milling time of 20 minutes) to obtain a sand-milled slurry; wherein the mass ratio of dimethylacetamide, ethylenediaminetetraacetic acid and lithium aluminum titanium phosphate as raw materials is 55:15:30.

[0040] The ethylenediaminetetraacetic acid is dispersed in the synthesized dimethylacetamide in an acidic manner and does not participate in the reaction during the following synthesis of aramid.

[0041] Step 2: Add the sand-milled slurry from step 1 to a reaction tank filled with nitrogen protective gas, add m-phenylenediamine to the equipment and stir for 20 minutes until dissolved, introduce cooling water into the equipment after dissolution and cool it to 0°C, add isophthaloyl chloride after cooling and stir for 20 minutes, remove the cooling water from the equipment, heat it to 80°C and stir for 80 minutes, and then add calcium hydroxide and stir for 30 minutes to obtain a mixed slurry from which hydrochloric acid in the reaction is removed; wherein the mass ratio of the sand-milled slurry, m-phenylenediamine, isophthaloyl chloride and calcium hydroxide as raw materials is 88:7:7:5, and the molar mass ratio of m-phenylenediamine to phthaloyl chloride is 1:1.

[0042] Step 3: Add dimethylacetamide to polyvinylidene fluoride and stir for 60 minutes to completely dissolve to obtain a mixed solution; wherein the mass ratio of polyvinylidene fluoride and dimethylacetamide as raw materials is 10:90.

[0043] Step 4: adding dimethyl carbonate pore-forming agent to the mixed slurry obtained in step 2 and stirring for 30 minutes to form a mixed solution; wherein the mass ratio of the mixed slurry obtained in step 2 and dimethyl carbonate as raw materials is 95:5.

[0044] In the step 4, hydrochloric acid is generated when the acyl chloride bond and the amide bond of isophthaloyl chloride and m-phenylenediamine are condensed during the polycondensation process. In order to eliminate the hydrochloric acid, calcium hydroxide is added during the synthesis process to offset the acidity of the hydrochloric acid. The calcium hydroxide not only offsets the hydrochloric acid in this process, but the free calcium ions therein will bind to the bond positions of the aramid, reducing the hydrogen bonds between the aramids. At this time, ethylenediaminetetraacetic acid will be adsorbed onto the calcium bound to the aramid. At this time, the oxygen on the coordination bond of ethylenediaminetetraacetic acid and the hydrogen in the aramid are hydrogen-bonded together, so that the aramid not only produces an adsorbable metal effect, but also makes the structure of the aramid itself linear. The relevant reaction structure is shown as follows: Figure 3 shown.

[0045] Step 5: Mix the mixed solution obtained in step 3 and the mixed solution obtained in step 4 and stir for 60 minutes to obtain a coating slurry; wherein the mass ratio of the mixed solution obtained in step 3 and the mixed solution obtained in step 4 as raw materials is 20:80.

[0046] In step 5, nano-lithium titanium aluminum phosphate is combined with dissolved polyvinylidene fluoride. At this time, the exposed titanium, aluminum, and lithium bonds on the lithium titanium aluminum phosphate are hydrogen-bonded with the fluorine on the polyvinylidene fluoride to form a pre-lithium-supplemented gel state with a special structure. When this state is combined with aramid, some of the exposed titanium and aluminum will produce hydrogen bonding effects with the aramid, causing it to adhere together.

[0047] The main organic matter in the coating slurry is dissolved in the polar solvent (dimethylacetamide) to form a homogeneous solution with a certain viscosity, in which the nano-scale lithium aluminum titanium phosphate is suspended to form a stable and uniform dispersion system with electrostatic balance.

[0048] Step 6: Place a polyethylene base film with a specification of 800mm×12μm on a coating machine equipped with the coating slurry prepared in step 5 for slit extrusion coating. After coating, it is pulled by a traction roller into an extraction tank with 10 small tanks about 1m deep for extraction. The first three small tanks in the small tank that come into contact with the base film extraction are filled with extracts mixed with deionized water and dimethylacetamide in different content ratios, and the other small tanks are filled with deionized water. Among them, the ratio of dimethylacetamide content in the first small tank, the second small tank and the third small tank of the first three small tanks is 60:40:20. The coated base film passes through the small tanks containing the first, second, and third extracts and ionized water in sequence.

[0049] The extracted base membrane is pulled by a traction roller into an oven using three hot rollers (diameter 400 mm, temperature 80°C) for drying and air heat (temperature 50°C) for drying to obtain a multiphase composite electrolyte membrane.

[0050] The process of step 6 is as follows: Figure 2 shown.

[0051] like Figure 1 As shown in the scanning electron microscope image of the surface of the multiphase composite electrolyte membrane prepared in Example 1, the polyvinylidene fluoride and the aramid fiber have overlapped with each other, the pores are relatively uniform, and a three-dimensional structure is presented on the electron microscope. The electrolyte infiltration efficiency of this structure is very high, and it can completely lock all free electrolytes. The ionic conductivity of the solid-gel composite electrolyte system formed is close to that of the liquid electrolyte, so it can be applied to some medium and high power batteries.

[0052] The multi-phase composite electrolyte membrane can enable the battery to obtain the gain effects of high-efficiency capture of metal ions, high temperature resistance and gel-state pre-replenishment of lithium.

[0053] Example 2

[0054] The steps for preparing nano-lithium aluminum titanium phosphate powder are as follows:

[0055] Step A, drying ammonium dihydrogen phosphate, lithium carbonate, aluminum oxide and titanium dioxide (temperature 180°C), taking out and cooling, and then using a ball mill for the first grinding (grinding speed of 500r / min, grinding time of 5h) to obtain a mixed powder, placing the mixed powder into a ceramic crucible, and then placing it into a muffle furnace for step-by-step heating and constant temperature (heating to 300°C, constant temperature for 2h, then continuing to heat to 500°C, constant temperature for 2h, heating again to 700°C, constant temperature for 2h, and finally heating to 900°C, constant temperature for 2h), taking out and cooling, crushing and performing a second grinding (grinding speed of 700r / min, grinding time for 15h) to obtain a ground powder; wherein, the mass ratio of ammonium dihydrogen phosphate, lithium carbonate, aluminum oxide and titanium dioxide as raw materials is 63:9:3:25.

[0056] Step B, adding the ground powder obtained in step A to ethanol, using a ball mill for ball milling (revolution speed of 300r / min, rotation speed of 700r / min, ball milling time of 15h) to obtain a mixed solution, and precipitating the mixed solution for 24h to obtain a precipitated mixed solution, wherein the precipitated mixed solution is divided into three layers, namely a precipitation layer (particle size of 0.5-2μm), an intermediate layer (particle size of 350nm) and a floating layer (particle size of 50-100nm), and the floating layer is taken out from the precipitated mixed solution, dried and ground to obtain nano-lithium aluminum titanium phosphate powder; wherein the mass ratio of ethanol and lithium aluminum titanium phosphate as raw materials is 50:50.

[0057] A method for preparing a multiphase composite electrolyte membrane based on ethylenediaminetetraacetic acid comprises the following steps:

[0058] Step 1: Add ethylenediaminetetraacetic acid to dimethylacetamide, stir for 35 minutes to obtain a mixed solution, ultrasonicate the mixed solution for 45 minutes (ultrasonic frequency of 150 Hz), then add nano-lithium aluminum titanium phosphate powder and ultrasonicate for 45 minutes (ultrasonic frequency of 150 Hz) to obtain an ultrasonically dispersed slurry, and sand-mill the ultrasonically dispersed slurry using a pin-type sand mill (speed of 700 r / min, sand-milling time of 25 minutes) to obtain a sand-milled slurry; wherein the mass ratio of dimethylacetamide, ethylenediaminetetraacetic acid and lithium aluminum titanium phosphate as raw materials is 52:13:35.

[0059] Step 2: Add the sand-milled slurry from step 1 to a reaction tank filled with nitrogen protective gas, add m-phenylenediamine to the equipment and stir for 20 minutes until dissolved, introduce cooling water into the equipment after dissolution and cool it to 3° C., add isophthaloyl chloride after cooling and stir for 20 minutes, remove the cooling water from the equipment, heat it to 80° C. and stir for 80 minutes, then add calcium hydroxide and stir for 30 minutes to obtain a mixed slurry from which hydrochloric acid in the reaction is removed; wherein the mass ratio of the sand-milled slurry, m-phenylenediamine, isophthaloyl chloride and calcium hydroxide as raw materials is 83:10:10:7, and the molar mass ratio of m-phenylenediamine to phthaloyl chloride is 1:1.

[0060] Step 3: Add dimethylacetamide to polyvinylidene fluoride and stir for 70 minutes to completely dissolve to obtain a mixed solution; wherein the mass ratio of polyvinylidene fluoride and dimethylacetamide as raw materials is 13:87.

[0061] Step 4: adding dimethyl carbonate pore-forming agent to the mixed slurry obtained in step 2 and stirring for 30 minutes to form a mixed solution; wherein the mass ratio of the mixed slurry obtained in step 2 and dimethyl carbonate as raw materials is 94:6.

[0062] Step 5: Mix and stir the mixed solution obtained in step 3 and the mixed solution obtained in step 4 for 70 minutes to obtain a coating slurry; wherein the mass ratio of the mixed solution obtained in step 3 and the mixed solution obtained in step 4 as raw materials is 25:75.

[0063] Step 6: Place a polyethylene 8 base film with a specification of 800mm×12μm on a coating machine equipped with the coating slurry prepared in step 5 for slit extrusion coating. After coating, it is pulled by a traction roller into an extraction tank with 10 small tanks about 1m deep for extraction. The first three small tanks in the small tank that come into contact with the base film extraction are filled with extracts mixed with deionized water and dimethylacetamide in different content ratios, and the other small tanks are filled with deionized water. Among them, the ratio of dimethylacetamide content in the first small tank, the second small tank and the third small tank of the first three small tanks is 60:40:20. The coated base film passes through the small tanks containing the first, second, and third extracts and ionized water in sequence.

[0064] The extracted base membrane is pulled by a traction roller into an oven using three hot rollers (diameter 500 mm, temperature 85°C) for drying and air heat (temperature 60°C) for drying to obtain a multiphase composite electrolyte membrane.

[0065] Example 3

[0066] A method for preparing a multiphase composite electrolyte membrane based on ethylenediaminetetraacetic acid comprises the following steps:

[0067] Step A, drying ammonium dihydrogen phosphate, lithium carbonate, aluminum oxide and titanium dioxide (temperature 200°C), taking out and cooling, and then using a ball mill for the first grinding (grinding speed of 500r / min, grinding time of 6h) to obtain a mixed powder, placing the mixed powder into a ceramic crucible, and then placing it into a muffle furnace for step-by-step heating and constant temperature (heating to 350°C, constant temperature for 2h, then continuing to heat to 550°C, constant temperature for 2h, heating again to 750°C, constant temperature for 2h, and finally heating to 950°C, constant temperature for 2h), taking out and cooling, crushing and performing a second grinding (grinding speed of 800r / min, grinding time for 24h) to obtain a ground powder; wherein, the mass ratio of ammonium dihydrogen phosphate, lithium carbonate, aluminum oxide and titanium dioxide as raw materials is 65:10:4:26.

[0068] Step B, adding the ground powder obtained in step A to ethanol, using a ball mill for ball milling (revolution speed of 400r / min, rotation speed of 800r / min, ball milling time of 24h) to obtain a mixed solution, and precipitating the mixed solution for 24h to obtain a precipitated mixed solution, wherein the precipitated mixed solution is divided into three layers, namely a precipitation layer (particle size of 2μm), an intermediate layer (particle size of 200-500nm) and a floating layer (particle size of 50-100nm), and the floating layer is taken out from the precipitated mixed solution, dried and ground to obtain nano-lithium aluminum titanium phosphate powder; wherein the mass ratio of ethanol and lithium aluminum titanium phosphate as raw materials is 30:70.

[0069] Step 1: Add ethylenediaminetetraacetic acid to dimethylacetamide, stir for 40 minutes to obtain a mixed solution, ultrasonicate the mixed solution for 50 minutes (ultrasonic frequency of 200 Hz), then add nano-lithium aluminum titanium phosphate powder and ultrasonicate for 50 minutes (ultrasonic frequency of 200 Hz) to obtain an ultrasonically dispersed slurry, and use a pin-type sand mill to sand grind the ultrasonically dispersed slurry (speed of 800 r / min, sand grinding time of 30 minutes) to obtain a sand-milled slurry; wherein the mass ratio of dimethylacetamide, ethylenediaminetetraacetic acid and lithium aluminum titanium phosphate as raw materials is 50:10:40.

[0070] Step 2: Add the sand-milled slurry from step 1 to a reaction tank filled with nitrogen protective gas, add m-phenylenediamine to the equipment and stir for 20 minutes until dissolved, introduce cooling water into the equipment after dissolution and cool to 5° C., add isophthaloyl chloride after cooling and stir for 20 minutes, remove the cooling water from the equipment, heat to 80° C. and stir for 80 minutes, then add calcium hydroxide and stir for 30 minutes to obtain a mixed slurry from which hydrochloric acid in the reaction is removed; wherein the mass ratio of the sand-milled slurry, m-phenylenediamine, isophthaloyl chloride and calcium hydroxide as raw materials is 78:12:12:10, and the molar mass ratio of m-phenylenediamine to phthaloyl chloride is 1:1.

[0071] Step 3: Add dimethylacetamide to polyvinylidene fluoride and stir for 80 minutes to completely dissolve to obtain a mixed solution; wherein the mass ratio of polyvinylidene fluoride and dimethylacetamide as raw materials is 15:85.

[0072] Step 4: adding dimethyl carbonate pore-forming agent to the mixed slurry obtained in step 2 and stirring for 30 minutes to form a mixed solution; wherein the mass ratio of the mixed slurry obtained in step 2 and dimethyl carbonate as raw materials is 93:7.

[0073] Step 5: Mix and stir the mixed solution obtained in step 3 and the mixed solution obtained in step 4 for 80 minutes to obtain a coating slurry; wherein the mass ratio of the mixed solution obtained in step 3 and the mixed solution obtained in step 4 as raw materials is 30:70.

[0074] Step 6: Place a polyethylene base film with a specification of 800 mm × 12 μm on a coating machine equipped with the coating slurry prepared in step 5 for slit extrusion coating. After coating, it is pulled by a traction roller into an extraction tank with 10 small tanks about 1 m deep for extraction. The first three small tanks in the small tank that come into contact with the base film extraction are filled with an extracting solution mixed with deionized water and dimethylacetamide in different content ratios, and the other small tanks are filled with deionized water. Among them, the ratio of the dimethylacetamide content in the first small tank, the second small tank and the third small tank of the first three small tanks is 60:40:20. The coated base film passes through the small tanks containing the first, second and third extraction solutions and ionized water in sequence.

[0075] The extracted base membrane is pulled by a traction roller into an oven using three hot rollers (diameter 600 mm, temperature 90°C) for drying and air heat (temperature 70°C) for drying to obtain a multiphase composite electrolyte membrane.

[0076] Comparative Example 1

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

[0078] Comparative Example 1 was obtained by replacing the lithium aluminum titanium phosphate in step 1 of Example 1 with aluminum oxide particles.

[0079] Comparative Example 2

[0080] A method for preparing a diaphragm comprises the following steps:

[0081] Comparative Example 2 was obtained by removing the ethylenediaminetetraacetic acid in step 1 of Example 1.

[0082] Comparative Example 3

[0083] A method for preparing a diaphragm comprises the following steps:

[0084] Comparative Example 3 was obtained by removing the polyvinylidene fluoride in step 3 of Example 1.

[0085] The membrane rupture temperature of the membranes prepared in Examples 1-3 and Comparative Examples 1-3 was tested using the following method:

[0086] The test membrane was made into a test sample (length 7.8 mm, width 5 mm) and tested using a dynamic thermomechanical analyzer (tensile force set to 0.1 N, heating rate 5 ° C / min); the test results are shown in the following table:

[0087] Table 1 Comparison of the membrane rupture temperature data provided by Examples 1-3 and Comparative Examples 1-3

[0088]

[0089] It can be seen from the above table that the embodiment diaphragm has good temperature resistance.

[0090] The diaphragms prepared in Examples 1-3 and Comparative Examples 1-3 were used to test the ability of the diaphragms to capture metal elements in batteries. The test method was as follows:

[0091] A trace amount of iron oxide powder (0.005% by mass) and manganese dioxide (0.005% by mass) were added to the electrolyte, and the two metal oxides were stirred evenly. The mixture was then added to a battery wound with the battery separators of Examples 1-3 and Comparative Examples 1-3 (battery thickness: 3.5 mm; width: 78 mm; height: 131 mm; nominal capacity: 4000 mAh; internal resistance: less than 40 mΩ; nominal voltage: 3.7 V; positive electrode: lithium iron phosphate; negative electrode: graphite; electrolyte: lithium hexafluorophosphate as solute; carbonate as solvent). The battery was cycled 20 times to discharge all its energy. The electrolyte was extracted and placed in an evaporating dish for drying. The dried solid was then fully dissolved in nitric acid and tested using an ICP spectrometer. The test results are shown in the following table:

[0092] Table 2 ICP spectrometer test results of batteries made of the diaphragms provided in Examples 1-3 and Comparative Examples 1-3

[0093] Element content (ppm) manganese iron Example 1 56 71 Example 2 62 68 Example 3 58 61 Comparative Example 1 6801 7523 Comparative Example 2 6805 7541 Comparative Example 3 6892 7556

[0094] Judging from the above test results, the diaphragm can obviously capture metal elements to form a complex reaction, thereby improving the safety performance of the battery.

[0095] The diaphragms prepared in Examples 1-3 and Comparative Examples 1-3 were tested for self-discharge in batteries. The test method was as follows:

[0096] A trace amount of iron oxide powder (0.005% by mass) and manganese dioxide (0.005% by mass) were added to the electrolyte, and the two metal oxides were stirred evenly. The mixture was then added to a battery wound with the battery separators of Examples 1-3 and Comparative Examples 1-3 (battery thickness: 3.5 mm; width: 78 mm; height: 131 mm; nominal capacity: 4000 mAh; internal resistance: less than 40 mΩ; nominal voltage: 3.7 V; positive electrode: lithium iron phosphate; negative electrode: graphite; electrolyte: lithium hexafluorophosphate as solute; carbonate as solvent). The battery was cycled 50 times and then fully charged. The self-discharge of the battery was tested over time. The test results are shown in the following table:

[0097] Table 3 Comparison of self-discharge data of the separators provided in Examples 1-3 and Comparative Examples 1-3 in the battery

[0098] Voltage (V) 10 days 20 days 30 days 40 days 50 days Example 1 3.5 3.5 3.3 3.1 3 Example 2 3.6 3.4 3.2 3.0 2.9 Example 3 3.6 3.5 3.3 3.2 2.7 Comparative Example 1 2.1 1.4 0.4 0.2 0 Comparative Example 2 2.0 0.4 0.6 0.1 0 Comparative Example 3 1.8 0.5 0.2 0.1 0

[0099] It can be seen from the data in the table that when the electrolyte contains iron, the self-discharge of the battery is very serious without treatment, while the self-discharge of the battery made in the embodiment is very small.

[0100] The diaphragms prepared in Examples 1-3 and Comparative Examples 1-3 were tested for voltage breakdown, and the test method was as follows:

[0101] The diaphragm was laid flat on the voltage breakdown test conductive plate, and 50 breakdown points were tested for each sample. The test results are shown in the following table:

[0102] Table 4 Diaphragm voltage breakdown test results provided by Examples 1-3 and Comparative Examples 1-3

[0103]

[0104] From the test results, it can be seen that the voltage breakdown of the embodiment is significantly higher than that of the comparative example.

[0105] The ion conductivity of the diaphragms prepared in Examples 1-3 and Comparative Examples 1-3 was tested using the following method:

[0106] The diaphragm was loaded onto the conductivity tester and each sample was tested. The test results are shown in the following table:

[0107] Table 5 Ionic conductivity test results of the membranes provided by Examples 1-3 and Comparative Examples 1-3

[0108] Examples / Comparative Examples impedance Ionic conductivity (mS / cm) Example 1 0.0331 1.4623 Example 2 0.0336 1.4612 Example 3 0.0338 1.4608 Comparative Example 1 0.0635 0.8102 Comparative Example 2 0.0624 0.8078 Comparative Example 3 0.0618 0.8795

[0109] The test results show that the introduction of lithium aluminum titanium phosphate solid electrolyte significantly improves the ionic conductivity of the gel coating. The increase in ionic conductivity can improve the charge and discharge efficiency of the battery.

[0110] In Comparative Example 1, when the lithium titanium aluminum phosphate is replaced by aluminum oxide, since the aluminum oxide is crystalline, it cannot generate hydrogen bonds with polyvinylidene fluoride and cannot combine with aramid to form a stable combination on the surface of the diaphragm, and cannot form a hydrogen bond structure. The polyvinylidene fluoride, aramid, and aluminum oxide exist separately, which increases the gaps in the coating and easily causes the voltage to break through the diaphragm, and also makes the coated diaphragm not have strong heat resistance, which ultimately leads to a low membrane rupture temperature; polyvinylidene fluoride covers the aramid, blocking the ability of ethylenediaminetetraacetic acid to adsorb metals; because aluminum oxide and polyvinylidene fluoride cannot form a hydrogen bond structure with aramid, they ultimately cannot combine with polyvinylidene fluoride to form a larger specific surface area, reducing its ability to capture metals; because the ability to capture metals is reduced, the metal will be oxidized at the positive electrode and then reduced at the negative electrode, forming hard metal edges that pierce the diaphragm, causing the battery to self-discharge.

[0111] In Comparative Example 2, after the ethylenediaminetetraacetic acid in the slurry is removed, hydrogen bonds cannot be generated between the hydrogen in the aramid and the oxygen on the coordination bond of the ethylenediaminetetraacetic acid, and the structure of the aramid itself cannot be made linear, and ultimately the aramid cannot have higher temperature resistance; the diaphragm loses its ability to capture metal, directly causing the metal to be oxidized at the positive electrode and then reduced at the negative electrode, resulting in self-discharge; since the bonds of the aramid are scattered and the molecular weight is reduced, the bonding performance of the diaphragm is reduced, and the voltage breakdown of the diaphragm is reduced.

[0112] In Comparative Example 3, when polyvinylidene fluoride is removed, the lithium titanium aluminum phosphate in the diaphragm will be scattered and cannot form a stable structure, resulting in reduced high temperature resistance and voltage breakdown of the diaphragm; when polyvinylidene fluoride is removed, because the lithium titanium aluminum phosphate does not form a gel carrier, the nanoparticles will react with ethylenediaminetetraacetic acid to produce a complexation reaction, causing the ethylenediaminetetraacetic acid therein to lose its ability to capture metals, causing the metal to be oxidized at the positive electrode and then reduced at the negative electrode, resulting in self-discharge.

[0113] By adjusting the process parameters according to the content of the present invention, the multiphase composite electrolyte membrane of the present invention can be prepared and exhibit performance basically consistent with that of the embodiment.

[0114] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a multiphase composite electrolyte membrane based on ethylenediaminetetraacetic acid, characterized in that: The following steps are involved: Step 1: Add ethylenediaminetetraacetic acid to dimethylacetamide and disperse evenly, then add nano-lithium aluminum titanium phosphate powder, disperse evenly, and sand grind to obtain a sand-milled slurry; Step 2: Add the sand-milled slurry from step 1 to a device filled with an inert protective gas, add m-phenylenediamine to dissolve it in the device, add isophthaloyl chloride to react fully, and then add calcium hydroxide to obtain a mixed slurry containing linear aramid fibers from which hydrochloric acid in the reaction has been removed; Step 3, adding dimethylacetamide to polyvinylidene fluoride and stirring to completely dissolve to obtain a mixed solution; Step 4, adding a pore-forming agent to the mixed slurry obtained in step 2 and stirring to obtain a mixed solution; Step 5, mixing the mixed solution obtained in step 3 with the mixed solution obtained in step 4 to obtain a coating slurry; In step 6, the base film is placed on a coating machine equipped with the coating slurry prepared in step 5 for uniform coating, and after coating, it is pulled into an extraction tank for extraction, and after extraction, it is pulled into an oven for drying to obtain a multiphase composite electrolyte membrane.

2. The preparation method according to claim 1, wherein In step 1, the method for preparing the nano-lithium aluminum titanium phosphate powder is as follows: diammonium dihydrogen phosphate, lithium carbonate, aluminum oxide and titanium dioxide in a mass ratio of (60-65): (8-10): (2-4): (24-26) are sintered to obtain a product, and then the product is mixed with ethanol in a mass ratio of (60-30): (40-70) and nano-sized to obtain nano-lithium aluminum titanium phosphate powder.

3. The preparation method according to claim 1, wherein In the step 1, ethylenediaminetetraacetic acid is added to dimethylacetamide, stirred for 30-40 minutes to obtain a mixed solution, the mixed solution is ultrasonicated for a first time, and then nano-lithium aluminum titanium phosphate powder is added and ultrasonicated for a second time to obtain an ultrasonically dispersed slurry, and the ultrasonically dispersed slurry is sand-milled to obtain a sand-milled slurry; wherein the mass ratio of dimethylacetamide, ethylenediaminetetraacetic acid, and lithium aluminum titanium phosphate as raw materials is (55-50): (15-10): (30-40).

4. The preparation method according to claim 3, wherein The sanding speed is 600-800 r / min and the sanding time is 20-30 min; the first ultrasound has an ultrasound frequency of 100-200 Hz and an ultrasound time of 40-50 min; the second ultrasound has an ultrasound frequency of 100-200 Hz and an ultrasound time of 40-50 min.

5. The preparation method according to claim 1, wherein In the step 2, the slurry obtained after sand milling in step 1 is added to a device filled with an inert protective gas, m-phenylenediamine is added to the device and stirred for the first time until dissolved, the temperature is lowered after dissolution, isophthaloyl chloride is added after cooling and stirred for the second time, the temperature is raised and stirred for the third time, and calcium hydroxide is added and stirred for the fourth time to obtain a mixed slurry containing linear aramid fiber from which hydrochloric acid in the reaction has been removed; wherein the mass ratio of the sand milled slurry, m-phenylenediamine, isophthaloyl chloride and calcium hydroxide as raw materials is (88-78): (7-12): (7-12): (5-10).

6. The preparation method according to claim 5, wherein The cooling process is to introduce cooling water into the equipment and cool it down to 0-5°C, and the heating process is to remove the cooling water from the equipment and heat it up to 60-80°C; the first stirring process has a stirring time of 20-50 minutes; the second stirring process has a stirring time of 20-50 minutes; the third stirring process has a stirring time of 30-80 minutes; and the fourth stirring process has a stirring time of 20-30 minutes.

7. The preparation method according to claim 1, wherein In the step 3, dimethylacetamide is added to polyvinylidene fluoride and stirred to completely dissolve to obtain a mixed solution; wherein the mass ratio of polyvinylidene fluoride and dimethylacetamide as raw materials is (10-15): (90-85).

8. The preparation method according to claim 1, wherein The stirring time in step 3 is 60 to 80 minutes.

9. The preparation method according to claim 1, wherein In the step 4, the mass ratio of the mixed slurry obtained in the step 2 and dimethyl carbonate as raw materials is (95-93): (5-7).

10. The preparation method according to claim 1, wherein The stirring time of step 4 is 15 to 30 minutes.

11. The preparation method according to claim 1, wherein In the step 5, the mixed solution obtained in step 3 and the mixed solution obtained in step 4 are mixed and stirred for 60 to 80 minutes to obtain a coating slurry; wherein the mass ratio of the mixed solution obtained in step 3 and the mixed solution obtained in step 4 as raw materials is (20 to 30): (80 to 70).

12. The preparation method according to claim 1, wherein The base film in step 6 is a polyethylene base film with a specification of 800 mm×12 μm; the coating is a slit extrusion coating.

13. The preparation method according to claim 1, wherein In step 6, the extraction tank is an extraction tank with 10 built-in small tanks; among the small tanks, the first three small tanks are filled with a mixture of dimethylacetamide and water, and the dimethylacetamide content ratio is 60:40:20; the other small tanks are filled with deionized water, and the oven is dried by hot roller drying and air heating drying; there are three hot rollers with a diameter of 400~600mm and a temperature set to 80~90℃; the air heating drying is set to a temperature of 50~70℃.

14. A multiphase composite electrolyte membrane based on ethylenediaminetetraacetic acid, characterized in that: The method is obtained by the preparation method according to any one of claims 1 to 13.

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