CN114583397A - A kind of functional diaphragm and its preparation method and application - Google Patents

Abstract

The invention discloses a functional diaphragm and a preparation method and application thereof, wherein the preparation method comprises the following steps: a base film; and a coating layer formed on a surface of the base film, the coating layer including a heat-resistant material, a high molecular polymer, and a solid electrolyte. Through set up the coating on the base film surface, this coating has fine adhesion between with the pole piece for the battery, and has higher ionic conductivity, and insulating properties and heat resistance are better simultaneously, and the difficult deformation internal resistance that utilizes this function diaphragm to assemble back is little, has better multiplying power and power performance, still has higher acupuncture and high temperature hot box security performance and better cycling performance simultaneously.

Description

A kind of functional diaphragm and its preparation method and application

technical field

The invention belongs to the technical field of lithium ion battery separators, in particular to a high-safety functional separator and a preparation method thereof, and also to a lithium ion battery with the functional separator.

Background technique

At present, lithium-ion batteries are the most frequently used choice in the new energy power battery industry, but at this stage, there are still abnormal safety problems such as battery thermal runaway leading to fire and explosion. The reasons and some battery abuse, such as overcharge and overdischarge, cause lithium ion inside the battery. Dendrite growth pierces the battery separator.

At present, the commonly used separators are mostly polyolefin materials, which have low melting point and poor heat resistance and poor puncture strength. When there is lithium deposition inside the battery or thermal runaway occurs due to an internal short circuit, the low strength of the internal separator of the battery will be dendrites. Puncture or abnormal shrinkage deformation due to heating of the separator further increases the internal temperature rise of the battery, resulting in frequent fire and explosion of the battery.

In order to improve the safety of lithium-ion batteries, the current main practice is to improve the conventional separators to improve the problem of poor safety of traditional separators. A common method is to coat the surface of the separator with a heat-resistant ceramic coating and/or a polymer coating to improve the heat resistance of the battery, but these methods have little effect on the thermal runaway caused by the battery.

SUMMARY OF THE INVENTION

In view of this, it is necessary for the present invention to provide a functional separator, the functional separator is formed with a coating layer on the surface of the base film, and the coating layer has good adhesion between the electrode sheet for the battery, and has a high High ionic conductivity, good insulation performance and heat resistance, the battery assembled with this functional separator is not easy to deform and has low internal resistance, good rate and power performance, and also has high acupuncture and high temperature hot box. Safety performance and better cycle performance.

In order to achieve the above object, the present invention adopts the following technical solutions:

The present invention provides a functional diaphragm, comprising:

basement membrane;

and a coating layer formed on the surface of the base film, the coating layer comprising a heat-resistant material, a high molecular polymer and a solid electrolyte.

In a further scheme, the heat-resistant material is selected from alumina, boehmite, silicon dioxide, magnesium hydroxide, titanium dioxide, magnesium oxide, barium sulfate, nanofibers, aramid, furan-based polyamide, polyethylene terephthalate A mixture of one or two or more of diester and polyimide.

In a further scheme, the high molecular polymer is selected from one or a mixture of two or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and polymethacrylate.

In a further solution, the solid electrolyte is selected from lithium aluminum titanium phosphate LATP.

The present invention further discloses a preparation method of the functional diaphragm as described in any of the foregoing, comprising the following steps:

adding the high molecular polymer to the solvent and mixing evenly to form a first mixed solution;

adding the heat-resistant material and the solid electrolyte into the first mixed solution and mixing uniformly to form a second mixed solution;

The second mixed solution is coated on the surface of the base film, treated with the solution and deionized water in sequence, and then dried to obtain a functional diaphragm.

In a further scheme, the solvent is selected from one of N-methylpyrrolidone (NMP), dimethylacetamide (DMAC), dimethylsulfoxide (DMSO) and N,N-dimethylformamide (DMF). one or a combination of two or more.

In a further solution, in the second mixed solution, the mass ratio of solvent: high molecular polymer: heat-resistant material: solid electrolyte is 100:3-5:3-6:3-8, and the slurry viscosity is 50-1000mpa ·s.

In a further scheme, the solution is a mixture of a solvent and deionized water in a mass ratio of (20-40):(20-60), and the passing speed of the coated membrane in the solution is 5-20 m/min.

In a further scheme, the passing speed of the coated membrane in deionized water is 10-30 m/min; the drying temperature is 50-70° C., and the speed of passing through the drying zone is 50-60 m/min.

The present invention further discloses a lithium ion battery, which includes a separator, wherein the separator is the functional separator described in any of the foregoing or the functional separator prepared by the preparation method described in any of the foregoing.

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

In the high-safety function separator of the present invention, a coating layer is formed on the surface of the base film, and the coating layer is obtained by compounding a heat-resistant material, a high molecular polymer and a solid electrolyte. Among them, the heat-resistant material in the coating layer has a good heat-resistant skeleton structure, and the interaction between the solvent and the non-solvent is used, so that the dissolved polymer can form a membrane layer with uniform pore size, and the selected polymer The polymer coating can form a good van der Waals force and anchoring force between the positive and negative plates of the battery, so that the separator and the pole pieces in the battery will not be displaced and deformed, and can prevent dust and foreign matter from entering the inside of the battery. At high temperature, the separator and the pole piece are integrated, which greatly reduces the high temperature thermal shrinkage of the separator and improves the safety performance of the battery's hot box. The ionic conductivity of the separator can be improved. On the one hand, the selection of LATP solid electrolyte greatly improves the ionic conductivity of the separator, and improves the battery rate and power performance; on the other hand, the decomposition temperature of LATP > 800 ℃ can also play a certain heat resistance, which is more important. What’s more, the corresponding negative electrode side of LATP material can change the valence of Ti from tetravalent to trivalent in the structure at low potential (<1.5V), and the consumption of Li ions in the process will form a solid-state electrolyte membrane layer similar to solid state electrolyte with the electrolyte, which reduces the energy consumption. The amount of liquid electrolyte in the cell prevents the formation of lithium dendrites in the battery, which greatly improves the safety performance and cycle life of the battery.

The functional separator and electrolyte in the present invention have good affinity, high ionic conductivity, good insulation performance and heat resistance, uniform pore size distribution, good porosity, coating layer and battery It has good adhesion between the pole pieces. The battery assembled with this diaphragm has no deformation and small internal resistance, good rate and power performance, good high temperature hot box safety performance and cycle performance, and excellent comprehensive performance. .

Detailed ways

The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, but should not be construed as limiting the present invention.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terms used herein in the description of the present invention are for the purpose of describing specific embodiments only, and are not intended to limit the present invention.

A first aspect of the present invention provides a functional separator comprising a base film and a coating layer formed on the surface of the base film. Wherein, the base film is not particularly limited, it is a conventional separator for lithium ion batteries in the field, and the material of the base film can be polyolefin such as polyethylene, polypropylene or polyethylene/polypropylene multilayer composite, or One of nanofibers, aramid fibers, furan-based polyamides, polyethylene terephthalate, and polyimide, which can be selected according to needs; the thickness of the base film is not particularly limited, and the Conventional thickness, according to an embodiment of the present invention, the thickness of the base film is between 3-20 μm, preferably 7-16 μm.

Further, the coating layer in the present invention can be formed on one side of the base film, or can be formed on both sides of the base film, and the thickness of one side can be the thickness of a conventional coating. The thickness of the layers is 1-6 μm. The coating layer includes a heat-resistant material, a high molecular polymer and a solid electrolyte, wherein the heat-resistant material is used in the coating layer to form a better heat-resistant skeleton structure, specific examples of which include but are not limited to oxidation One of aluminum, boehmite, silica, magnesium hydroxide, titanium dioxide, magnesium oxide, barium sulfate, nanofiber, aramid fiber, furan-based polyamide, polyethylene terephthalate, polyimide or a mixture of two or more. The dissolved state of the polymer used in this paper can form a membrane layer with uniform pore size, which has good van der Waals force and anchoring force between the positive and negative electrode sheets for batteries, and avoids the dislocation and deformation of the pole pieces. It is integrated, which greatly reduces the high temperature thermal shrinkage of the separator and improves the relative safety performance of the battery's hot box. At the same time, the high molecular polymer has a good affinity and liquid retention effect on the electrolyte, which can improve the ionic conductivity of the separator. Specific examples of which can be mentioned include, but are not limited to, one or a mixture of two or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and polymethacrylate. Further, the solid electrolyte in this paper is lithium aluminum titanium phosphate LATP, which on the one hand improves the ionic conductivity of the functional separator, improves the rate and power performance of the battery, and on the other hand provides a certain heat resistance and avoids lithium dendrites. It can greatly improve the safety performance and cycle life of lithium-ion batteries.

The second aspect of the present invention provides a preparation method of the functional diaphragm as described in the first aspect of the present invention, and the main steps are as follows:

The high molecular polymer is added to the solvent and mixed uniformly to form the first mixed solution; then the heat-resistant material and the solid electrolyte are added to the first mixed solution and mixed uniformly to form the second mixed solution. Among them, the selection of the solvent is based on the fact that it can dissolve the high molecular polymer, but not the heat-resistant material and the solid electrolyte. It can dissolve the high molecular polymer and realize the dispersion of the heat-resistant material and the solid electrolyte. Specifically, it can be mentioned that Examples are one or more of N-methylpyrrolidone (NMP), dimethylacetamide (DMAC), dimethylsulfoxide (DMSO) and N,N-dimethylformamide (DMF) the mix of. According to an embodiment of the present invention, in the second mixed solution, the mass ratio of solvent: high molecular polymer: heat-resistant material: solid electrolyte is 100: 3-5: 3-6: 3-8, and the slurry viscosity is 100: 3-5: 3-6: 3-8 50-1000mpa·s, it can be understood that the porosity of the coating layer on the surface of the base film can be adjusted by adjusting the proportional relationship and the viscosity of the slurry. The uniform mixing described herein is a conventional method in the art. In some embodiments of the present invention, a high-speed dispersant or a sand mill is used for mixing and dispersing.

Then, the second mixed solution is coated on the surface of the base film, treated with the solution and deionized water in sequence, and then dried to obtain a functional diaphragm. It can be understood that the coating process described herein is a conventional means in the art, such as microgravure transfer coating, etc., and will not be described in detail. The membrane after coating is processed by solution and deionized water successively, wherein, the solution is the use solvent of mass ratio 20-40:20-60 (the use solvent here is the same as the solvent adopted in the first mixed solution) and deionized water. The mixing of water can be automated with the diaphragm process. In some specific embodiments of the present invention, the passing speed of the coated diaphragm in the solution is 5-20 m/min; The passing speed is 10-30m/min; the drying temperature is 50-70°C, and the speed of passing through the drying zone is 50-60m/min. The coated separator is first passed through the solution to remove the solvent in the coating, and pores are formed in the coating where the solvent leaves the coating; then deionized water is passed to further remove the solvent in the coating and cure The morphology of the coating, and finally by drying the coating, a porous state will be formed, and the pores can play a role in transporting ions in the battery.

A third aspect of the present invention provides a lithium ion battery, comprising a separator, wherein the separator is the functional separator described in the first aspect of the present invention or a functional separator prepared by the preparation method described in the second aspect of the present invention .

Li-ion batteries assembled with the above functional separators have high safety and excellent cycle life.

The present invention will be described below through specific embodiments. It should be noted that the following specific embodiments are only for the purpose of illustration, and do not limit the scope of the present invention in any way. In addition, unless otherwise specified, conditions are not specifically described Or the methods of the steps are all conventional methods, and the reagents and materials used can be obtained from commercial sources; in the following examples and comparative examples, unless otherwise specified, the "parts" and "parts" refer to parts by mass. .

Example 1

Add 3 parts of polyvinylidene fluoride into 100 parts of NMP solvent, and use a high-speed disperser to disperse to form a uniform first mixed solution; then add 3 parts of alumina and 3 parts of LATP to the first mixed solution, and continue to disperse evenly to form a uniform first mixed solution. The second mixed solution; the second mixed solution is coated on both sides of the 12PE substrate (the thickness of one side is 4 μm); the coated separator is passed through NMP at a rate of 10m/min: deionized water is 20:30 15 m/min of deionized water, and finally dried in a 60°C high-precision oven at a rate of 50 m/min to obtain a high-safety functional diaphragm.

Example 2

Add 4 parts of polyvinylidene fluoride-hexafluoropropylene into 100 parts of DMAC solvent, and use a sand mill to disperse to form a uniform first mixed solution; then add 5 parts of boehmite and 5 parts of LATP to the first mixed solution, Continue to disperse evenly to form the second mixed solution; the second mixed solution is coated on both sides of the 12PP substrate (the thickness of one side is 3 μm); the coated diaphragm passes through DMAC at a speed of 20m/min: deionized water 30:40 parts of the solution, then passed through deionized water at a rate of 30m/min, and finally dried in a 70°C high-precision oven at a rate of 60m/min to obtain a high-safety functional diaphragm.

Example 3

Add 5 parts of polymethacrylate into 100 parts of DMF solvent, use a high-speed disperser to disperse to form a uniform first mixed solution; then add 6 parts of nanofibers and 8 parts of LATP to the first mixed solution, continue to disperse evenly, The second mixed solution was formed; the second mixed solution was single-sidedly coated on a 12PET substrate (with a thickness of 2 μm); the coated separator passed through DMF at a speed of 15 m/min: deionized water was 40:60 parts The solution is then passed through deionized water at a rate of 20 m/min, and finally dried in a high-precision oven at 55 °C at a rate of 50 m/min to obtain a high-safety functional diaphragm.

Comparative Example 1

This comparative example adopts the same embodiment as Example 1, except that no alumina is added. Other processes are the same as in Example 1.

Comparative Example 2

This comparative example adopts the same embodiment as in Example 1, except that no polyvinylidene fluoride is added. Other processes are the same as in Example 1.

Comparative Example 3

This comparative example adopts the same embodiment as in Example 1, except that LATP is not added. Other processes are the same as in Example 1.

test case

1. The functional diaphragms prepared in Examples 1-3 and Comparative Examples 1-3 and the double-sided coated 12PE+3+3 alumina ceramics+1+1 water-based glued diaphragms commonly used in the industry at present (denoted as comparison) Diaphragm), refer to the standard GB/T36363-2018 6.6.2 test method for ionic conductivity and 6.5.2 method for high temperature thermal shrinkage test.

Specifically, according to the same sample preparation method, the separator to be tested, the negative electrode sheet, the separator to be tested, and the positive electrode sheet are formed into a unit chip sample, and then the unit chip is heat-pressed under the test conditions of 80°C and 0.3mm roll gap, and the composite unit Piece samples, the width of each test sample is 15mm, and the length is slightly larger than the length of the steel plate. Samples are prepared in the order of steel plate/3M double-sided tape/pole piece/diaphragm, and about 15cm of ordinary tape is reserved at the end of the diaphragm (must be larger than The length of the steel plate), use a high-precision tensile machine to wait to test the adhesion between the coating and the pole piece. The test results are shown in Table 1.

Table 1 Test results of physical and chemical properties of functional separators

From the test results in Table 1, it can be seen that compared with Comparative Example 1-3, the high temperature heat shrinkage performance of the separator in Comparative Example 1 is reduced, and the coated separator in Comparative Example 2 loses the adhesion of the coating Force function, the ionic conductivity of the coated separator in Comparative Example 3 decreased. The functional separators in Examples 1-3 have higher ionic conductivity than the current general-purpose separators, which can greatly improve the rate and power performance of the battery. Good high temperature heat resistance, the high heat resistance diaphragm under the same battery phase difference can improve the heat-related safety performance of the battery, and at the same time, the adhesion between the coating and the pole piece is high, and when the diaphragm in the battery is thermally deformed It will be integrated, and the positive and negative plates will not be short-circuited in a large range due to the single deformation of the diaphragm, which can greatly improve the safety performance of the battery.

2. The high-safety function diaphragms prepared in Examples 1-3 and Comparative Examples 1-3 and the double-sided coated 12PE+3+3 alumina ceramics+1+1 water-based glued diaphragms commonly used in the industry at present (denoted as Comparative separator), the same high energy density battery design was used for trial production to obtain Example 1-3 battery, Comparative Example 1-3-battery and Comparative separator-battery, wherein the membrane coating layer was designed and trial-produced for the negative electrode to obtain the experimental battery, each selection The two batteries were overcharged according to 6.2.3 of GBT 31485-2015, and charged with a constant current of 1A until the voltage reached 1.5 times the end-of-charge voltage. Refer to the standard DB 34/T 3377-2019 for testing. After the experimental battery is fully charged, it is preheated in the adiabatic cavity of the accelerated adiabatic calorimeter. The temperature at the geometric center of the battery front is used as the reference temperature, and the battery temperature is heated within <3h When the temperature reaches 50 °C, stand for 45 minutes and observe the temperature change of the battery for 10 minutes; if the temperature rise rate of the battery itself is less than 0.02 °C/min, the temperature rises by 3 °C until the temperature rise rate of the battery is greater than 0.02 °C/min, the battery enters a self-heating state , record the temperature at this time as the exothermic starting temperature of the lithium-ion battery; after the lithium-ion battery enters the self-exothermic state, continue to record the temperature change until the temperature rise rate of the battery reaches 1 °C/min, and record the temperature at this time as the critical temperature; When the temperature rise rate of the battery reaches 10°C/min, the temperature at this time is recorded as the thermal runaway temperature; the temperature continues to rise after the battery catches fire and explodes, and the highest temperature recorded is the thermal runaway maximum temperature record, and the battery stops after thermal runaway occurs. During the test, if the battery does not experience thermal runaway, stop the test when the temperature reaches the termination temperature of 310°C, and stand for observation for 2 hours. The test results are shown in Table 2 below.

Table 2 Thermal runaway test results of experimental batteries

The test results of the battery of Example 1-3 and the battery of the comparative example showed that no thermal runaway occurred in the battery of Example 1-3, and the exothermic onset temperature, critical temperature, thermal runaway temperature, and maximum temperature were higher than those of the comparative diaphragm battery, which further explained the implementation. Example 1-3 The high-safety function separator used in the battery has good safety performance, and the battery will not further run out of control when the superimposed temperature rise inside the battery reaches about 260°C. However, in Comparative Examples 1-3, the thermal runaway performance test of the diaphragm and the comparative diaphragm battery was carried out in an overcharged state. The internal exothermic starting temperature was low, and the interval between the critical temperature and the thermal runaway temperature was small, indicating that the internal thermal runaway of the battery was caused. The rate is relatively fast, the maximum temperature of the battery reaches about 800 ℃, and the battery thermal runaway explosion occurs. It can be seen from the above comparison that this is due to the coordination of the three components in the coating, wherein the heat-resistant material provides a heat-resistant skeleton structure; the dissolved high molecular polymer forms a membrane layer with uniform pore size, which makes the isolation membrane and The pole pieces are integrated, which greatly reduces the high temperature thermal shrinkage of the separator and improves the relative safety performance of the battery's hot box. In addition, the high molecular polymer in the coating will bond the pole pieces together in the battery. When heat is generated internally, this force will slow down the thermal shrinkage of the separator to a certain extent, and can also play a role in heat resistance; with the LATP material corresponding to the negative side, four Ti formation can occur in the structure at low potential (<1.5V). In the process of changing the valence from valence to trivalence, the consumption of Li ions and the electrolyte will form a solid electrolyte membrane layer similar to solid state, which reduces the amount of liquid electrolyte in the battery cell, and will not form lithium dendrites in the battery, which can greatly avoid The occurrence of battery thermal runaway greatly improves the safety performance and cycle life of the battery. In addition, the solvent method preparation process adopted in the present invention can mix the above three components more uniformly, the adhesive force between the prepared high molecular polymer material and the pole piece is good, and the effect of the coating layer is more fully exerted.

The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be regarded as the scope described in this specification.

The above-mentioned embodiments only represent several embodiments of the present invention, and the descriptions thereof are specific and detailed, but should not be construed as a limitation on the scope of the invention patent. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims (10)

1. A functional separator, comprising:

a base film;

and a coating layer formed on a surface of the base film, the coating layer including a heat-resistant material, a high molecular polymer, and a solid electrolyte.

2. The functional separator according to claim 1, wherein the heat-resistant material is one or a mixture of two or more selected from the group consisting of alumina, boehmite, silica, magnesium hydroxide, titanium dioxide, magnesium oxide, barium sulfate, nanofiber, aramid, furan-based polyamide, polyethylene terephthalate, and polyimide.

3. The functional separator according to claim 1, wherein the high molecular polymer is one or a mixture of two or more selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and polymethacrylate.

4. The functional separator of claim 1 wherein said solid electrolyte is selected from lithium aluminum titanium phosphate LATP.

5. A method for preparing a functional separator according to any of claims 1 to 4, comprising the steps of:

adding a high molecular polymer into a solvent, and uniformly mixing to form a first mixed solution;

adding a heat-resistant material and a solid electrolyte into the first mixed solution, and uniformly mixing to form a second mixed solution;

and coating the second mixed solution on the surface of the base membrane, sequentially treating the base membrane by using solution and deionized water, and drying to obtain the functional diaphragm.

6. The method according to claim 5, wherein the solvent is one or a mixture of two or more selected from the group consisting of N-methylpyrrolidone (NMP), Dimethylacetamide (DMAC), Dimethylsulfoxide (DMSO), and N, N-Dimethylformamide (DMF).

7. The method according to claim 5, wherein, in the second mixed solution, a ratio of a solvent: high molecular weight Polymer: heat-resistant material: the mass ratio of the solid electrolyte is 100: 3-5: 3-6: 3-8, and the viscosity of the slurry is 50-1000mpa · s.

8. The method according to claim 5, wherein the solution is prepared by mixing, in a mass ratio (20-40): (20-60) using a mixture of a solvent and deionized water, the passing rate of the coated separator in the solution is 5-20 m/min.

9. The method of claim 5, wherein the coated separator has a passing speed of 10 to 30m/min in deionized water; the drying temperature is 50-70 deg.C, and the speed of drying is 50-60 m/min.

10. A lithium ion battery comprising a separator, wherein the separator is the functional separator according to any one of claims 1 to 4 or the functional separator prepared by the preparation method according to any one of claims 5 to 9.