Difunctional lithium battery diaphragm with high heat resistance and capability of inhibiting lithium dendrites and preparation method of difunctional lithium battery diaphragm

Abstract

The invention discloses a high-heat-resistance lithium dendrite inhibiting difunctional lithium battery diaphragm and a preparation method thereof.The lithium battery diaphragm comprises a base membrane and a coating on the base membrane, the coating comprises porous aluminum oxide, hydrated aluminum silicate, ammonium polyacrylate and an acrylate copolymer, the hydrated aluminum silicate is of a needle-shaped structure, the length of the hydrated aluminum silicate is 5-20 microns, the width of the hydrated aluminum silicate is 200-500 nm, and the thickness of the hydrated aluminum silicate is 10-20 microns. And the thickness is 50-200nm. The specific surface area of the porous alumina is 10-15m < 2 > / g, and the pore diameter is 5-10nm. According to the preparation method, the porous aluminum oxide and the hydrated aluminum silicate are mixed, so that the linear needle-shaped hydrated aluminum silicate can be arranged in a crossed manner to form a unique skeleton structure, the skeleton structure is like a fine and stable grid, and ideal attachment sites and support frames are provided for the porous aluminum oxide, so that the porous aluminum oxide is effectively fixed. The lithium battery diaphragm disclosed by the invention has excellent heat resistance, and the coating and the base membrane are tightly connected.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery separators, and specifically relates to a dual-functional lithium-ion battery separator with high heat resistance and inhibition of lithium dendrites and a preparation method thereof. Background Art

[0002] With the continuous increase in the global demand for clean energy, lithium-ion batteries have been widely used in many fields due to their advantages such as high energy density and long cycle life. However, lithium-ion batteries also face many challenges during the rapid development process. On the one hand, the safety of the battery has attracted much attention. During the charging and discharging process of the battery, especially under abnormal conditions such as high temperature environment or overcharging and over-discharging, traditional lithium-ion battery separators are prone to thermal shrinkage, resulting in short circuit between the positive and negative electrodes, and then causing thermal runaway of the battery, seriously threatening the safety of users. Therefore, developing a lithium-ion battery separator with high heat resistance has become an urgent problem to be solved. On the other hand, the growth of lithium dendrites is one of the key factors affecting the performance and life of lithium-ion batteries. The formation of lithium dendrites not only damages the solid electrolyte interface film, causing loss of active substances, but also may pierce the separator, making the positive and negative electrodes directly contact, triggering a short circuit, and reducing the cycle stability and safety of the battery. Existing preparation methods of lithium-ion battery separators often have difficulty in simultaneously achieving high heat resistance and inhibition of lithium dendrites. Some high heat-resistant separators may not be effective in inhibiting the growth of lithium dendrites, while separators focusing on inhibiting the growth of lithium dendrites may have shortcomings in heat resistance performance. Therefore, it is of great significance to develop a lithium-ion battery separator with both high heat resistance and inhibition of lithium dendrites. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a lithium-ion battery separator.

[0004] Another object of the present invention is to provide a preparation method of the above lithium-ion battery separator.

[0005] Another object of the present invention is to provide a slurry.

[0006] The object of the present invention is achieved by the following technical solutions.

[0007] A lithium-ion battery separator, comprising: a base film and a coating on the base film, and the coating includes: porous alumina, hydrated aluminum silicate, ammonium polyacrylate, and acrylate copolymer. By mass, the ratio of porous alumina, hydrated aluminum silicate, ammonium polyacrylate, and acrylate copolymer is (10 - 20):(10 - 20):(0.2 - 0.5):(1 - 4).

[0008] In the above technical solution, the hydrated aluminum silicate has a needle-like structure, the length of the hydrated aluminum silicate is 5 - 20 μm, the width is 200 - 500 nm, and the thickness is 50 - 200 nm.

[0009] In the above technical solution, the specific surface area of the porous alumina is 10 - 15 m 2 / g, and the pore diameter is 5 - 10 nm.

[0010] The method for preparing the above lithium battery separator includes: coating a slurry on a base film, drying, and forming a coating on the base film to obtain the lithium battery separator.

[0011] In the above technical solution, the coating speed is 20 - 40 m / min.

[0012] In the above technical solution, the thickness of the coating is 2 - 3 μm.

[0013] In the above technical solution, the drying temperature is 40 - 60 °C, and the drying time is 5 - 10 min.

[0014] A slurry includes: porous alumina, hydrated aluminum silicate, water, a dispersant, and a binder. By mass, the ratio of porous alumina, hydrated aluminum silicate, the water, the dispersant, and the binder is (10 - 20):(10 - 20):(50 - 60):(0.2 - 0.5):(5 - 10).

[0015] In the above technical solution, preferably by mass, the ratio of porous alumina, hydrated aluminum silicate, the water, the dispersant, and the binder is (18 - 20):(10 - 12):(55 - 60):(0.2 - 0.5):(8 - 10).

[0016] In the above technical solution, the dispersant is ammonium polyacrylate.

[0017] In the above technical solution, the binder is an acrylate copolymer solution, and the content of the acrylate copolymer in the acrylate copolymer solution is 20 - 40 wt%.

[0018] In the above technical solution, the particle size of the slurry is: D50 = 0.4 - 0.7 microns, D90 = 0.9 - 1.6 microns.

[0019] A method for preparing a slurry includes: mixing porous alumina, hydrated aluminum silicate, water, a dispersant, and a binder until uniform to obtain the slurry. By mass, the ratio of porous alumina, hydrated aluminum silicate, the water, the dispersant, and the binder is (10 - 20):(10 - 20):(50 - 60):(0.2 - 0.5):(5 - 10).

[0020] In the above technical solution, the method for preparing the slurry specifically includes the following steps:

[0021] Step 1, mixing the water and the dispersant until uniform to obtain a first solution;

[0022] In step 1, water and a dispersant are mixed and stirred until homogeneous to obtain a first solution. The rotation speed of stirring is 500 - 1500 r / min, the revolution speed is 30 - 50 r / min, and the stirring time is 10 - 20 minutes.

[0023] Step 2, the first solution, hydrated aluminum silicate, and porous alumina are mixed until homogeneous to obtain a second solution;

[0024] In step 2, the first solution, hydrated aluminum silicate, and porous alumina are mixed and stirred until homogeneous to obtain a second solution. The rotation speed of stirring is 1500 - 2500 r / min, the revolution speed is 30 - 50 r / min, and the stirring time is 20 - 30 minutes.

[0025] Step 3, the second solution and a binder are mixed until homogeneous to obtain a slurry.

[0026] In step 3, the second solution and a binder are mixed, and simultaneously stirred and ultrasonicated for 5 - 10 minutes in a vacuum environment until homogeneous to obtain a slurry, wherein the vacuum degree of the vacuum environment is 500 - 1500 pa. The rotation speed of stirring is 1500 - 2500 r / min, the revolution speed of stirring is 30 - 50 r / min, and the ultrasonic frequency of ultrasonication is 5 - 10 kHz.

[0027] Application of hydrated aluminum silicate and porous alumina in synergistically improving the liquid absorption rate, liquid retention rate, ionic conductivity, needle punching strength, and / or peel strength of a separator.

[0028] Application of hydrated aluminum silicate and porous alumina in synergistically reducing the shrinkage rate, interfacial resistance, and / or contact angle of a separator.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] In the present invention, by mixing porous alumina and hydrated aluminum silicate, the linear needle-like hydrated aluminum silicate can be cross-arranged to form a unique skeleton structure. This skeleton structure is like a fine and stable grid, providing ideal attachment sites and a support framework for porous alumina (spherical-like particles), greatly enhancing the interaction force between them, thereby effectively fixing the porous alumina and significantly improving the adhesion between the coating and the base film; porous alumina has a large number of nano-pores, which can reduce the resistance of ion transport, and the ionic conductivity of the separator is improved; and porous alumina has a relatively high surface energy (the surface energy of porous alumina is 50 - 70 mJ / m 2) can enable the liquid to spread evenly on its surface, improve the wettability of the separator to ensure the uniform distribution of the electrolyte; the lithium-ion battery separator of the present invention has high mechanical strength and can withstand the impact brought by the change of the electrode material; in a high-temperature environment, the porous alumina can maintain its structural integrity, thereby improving the heat resistance of the separator and enabling it to adapt to a more severe temperature environment. This makes the overall performance of the separator better, the stability stronger, and the service life longer. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the lithium-ion battery separator prepared in Example 4;

[0032] Figure 2 (a) is the electrolyte contact angle of the base film, Figure 2 (b) is the electrolyte contact angle of the lithium-ion battery separator prepared in Example 4;

[0033] Figure 3 It is a cross-sectional scanning electron microscope image of the lithium-ion battery separator prepared in Comparative Example 6;

[0034] Figure 4 It is a cross-sectional scanning electron microscope image of the lithium-ion battery separator prepared in Example 4. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The technical solutions of the present invention will be further described below with specific embodiments.

[0036] Hydrated aluminum silicate (powder): Hubei Chengfeng Chemical Co., Ltd.;

[0037] Porous alumina (powder): Suzhou Jinyi New Material Technology Co., Ltd.;

[0038] Acrylate copolymer (polymerized from acrylate and vinylidene fluoride) solution: Ningbo Xinfei Plastic Chemical Co., Ltd.;

[0039] Ammonium polyacrylate: Shanghai Sanrui High Polymer Materials Technology Co., Ltd.

[0040] Porous alumina:

[0041]

[0042] Hydrated aluminum silicate:

[0043]

[0044] Double planetary mixer: XFZH-30L.

[0045] The water in the following examples is pure water.

[0046] In the following comparative examples, D10 = 0.335 μm, D50 = 0.527 μm, D90 = 1.089 μm for the conventional alumina (powder), the specific surface area is 8.43 m 2 / g, and the pore size is 6.5 nm.

[0047] In the following examples, the base film is a PE film, and the thickness of the base film is 7 μm.

[0048] Ionic conductivity: The test temperature is 25 °C and the relative humidity is 50%.

[0049] Peeling strength: Prepare a diaphragm with a width of 10 - 25 mm and a length of 150 mm as a sample. Use 3M transparent tape to paste on the coated surface of the sample, and leave enough length of the peeling end (at least 20 mm) for the 3M transparent tape. Use a standard roller to evenly press over the sample 3 times. Fix the two ends of the sample in the upper and lower jigs respectively, and the peeling direction is 180°. Use a tensile machine to tear one end of the 3M transparent tape at a speed of 100 mm / min to obtain the peeling strength.

[0050] Examples 1 - 3 and Comparative Example 4

[0051] A method for preparing a slurry, comprising the following steps:

[0052] Step 1: Mix water and a dispersant in a double planetary mixer and stir until uniform to obtain a first solution. Among them, the rotation speed of the stirring is 1000 r / min, the revolution speed is 40 r / min, the stirring time is 20 minutes, and the dispersant is ammonium polyacrylate;

[0053] Step 2: Add hydrated aluminum silicate and porous alumina to the first solution and stir until uniform to obtain a second solution. Among them, the rotation speed of the stirring is 2000 r / min, the revolution speed is 40 r / min, the stirring time is 30 minutes. The hydrated aluminum silicate has a needle-like structure, the length of the hydrated aluminum silicate is 10 μm, the width is 300 nm, and the thickness is 100 nm;

[0054] Step 3: Add a binder to the second solution, and stir and ultrasonically vibrate for 5 minutes until uniform in a vacuum environment to obtain a slurry. Among them, the vacuum degree of the vacuum environment is 1000 pa, the rotation speed of the stirring is 2000 r / min, the revolution speed of the stirring is 40 r / min, the ultrasonic frequency of the ultrasonic vibration is 5 kHz, the binder is an acrylate copolymer solution, and the content of the acrylate copolymer in the acrylate copolymer solution is 30 wt%. By mass fraction, the ratio of porous alumina, hydrated aluminum silicate, water, dispersant, and binder is X.

[0055] The value of X is shown in Table 1.

[0056] Table 1

[0057] Slurry X Example 1 20：10：60：0.5：9.5 Example 2 10：20：60：0.5：9.5 Example 3 15：15：60：0.5：9.5 Comparative Example 4 25：5：60：0.5：9.5

[0058] The particle sizes of the slurries prepared in Example 1 were: D50 = 0.532 μm, D90 = 1.467 μm; the particle sizes of the slurries prepared in Example 2 were: D50 = 0.587 μm, D90 = 1.542 μm; the particle sizes of the slurries prepared in Example 3 were: D50 = 0.475 μm, D90 = 1.453 μm; the particle sizes of the slurries prepared in Comparative Example 4 were: D50 = 0.458 μm, D90 = 1.341 μm.

[0059] Comparative Example 1

[0060] A method for preparing a slurry, comprising: mixing pure water and a dispersant in a double planetary mixer, first stirring at a rotation speed of 1000 r / min and a revolution speed of 40 r / min for 20 minutes to obtain Solution A, adding conventional alumina (powder) to Solution A, first stirring at a rotation speed of 2000 r / min and a revolution speed of 40 r / min for 30 minutes, and then sonicating at a frequency of 5 kHz for 5 minutes until uniform to obtain Solution B, adding a binder to Solution B, and simultaneously stirring and sonicating in a vacuum environment for 10 minutes until uniform (the vacuum degree of the vacuum environment is 1000 Pa, the rotation speed of stirring is 2000 r / min, the revolution speed of stirring is 40 r / min, and the ultrasonic frequency of sonication is 5 kHz) to obtain the slurry. By mass fraction, the ratio of conventional alumina, pure water, dispersant, and binder is 30:60:0.5:9.5. In this comparative example, the binder and the dispersant are the same as those in Example 1 respectively.

[0061] The particle sizes of the slurry prepared in Comparative Example 1 were: D50: 0.487 μm; D90: 1.335 μm.

[0062] Comparative Example 2

[0063] A method for preparing a slurry is basically the same as that in Comparative Example 1, the difference being only that: "conventional alumina" is replaced by "porous alumina".

[0064] The particle sizes of the slurry prepared in Comparative Example 2 were: D50: 0.421 μm; D90: 1.135 μm.

[0065] Comparative Example 3

[0066] A method for preparing a slurry is basically the same as that in Example 1, the difference being only that: "porous alumina" is replaced by "conventional alumina".

[0067] Examples 4 - 6 and Comparative Examples 5 - 8

[0068] A preparation method of a lithium battery separator includes: placing a base film on a coater, coating the slurry on the base film unidirectionally at a speed of 30 m / min, entering a drying device under the traction of a traction roller, drying at 60 °C for 10 minutes, forming a coating on the base film, and obtaining the lithium battery separator. The slurry is one of those in Examples 1 to 3 and Comparative Examples 1 to 4.

[0069] Table 2

[0070] Lithium battery separator Slurry used for preparing lithium battery separator Example 4 Example 1 Example 5 Example 2 Example 6 Example 3 Comparative Example 5 Comparative Example 1 Comparative Example 6 Comparative Example 2 Comparative Example 7 Comparative Example 3 Comparative Example 8 Comparative Example 4

[0071] The test parameters of the lithium battery separator prepared in Example 4 are as follows:

[0072]

[0073]

[0074] The test parameters of the lithium battery separator prepared in Example 5 are as follows:

[0075]

[0076] The test parameters of the lithium battery separator prepared in Example 6 are as follows:

[0077]

[0078]

[0079] The test parameters of the lithium battery separator prepared in Comparative Example 5 are as follows:

[0080]

[0081] The test parameters of the lithium battery separator prepared in Comparative Example 6 are as follows:

[0082]

[0083]

[0084] The test parameters of the lithium battery separator prepared in Comparative Example 7 are as follows

[0085]

[0086] The test parameters of the lithium battery separator prepared in Comparative Example 8 are as follows

[0087]

[0088]

[0089] Figure 1 It is a schematic diagram of the lithium battery separator prepared in Example 4 ( Figure 1In it, "PE separator" represents the base film. Doping linear needle-like hydrated aluminum silicate can form a framework structure, which is beneficial to fixing porous alumina (spherical-like particles), improving the adhesion between the coating and the base film, and the needle-like structure can provide additional lithium-ion transport channels, making the transport distribution of lithium ions more uniform.

[0090] Figure 2 (a) of it is the electrolyte contact angle of the base film. Figure 2 (b) of it is the electrolyte contact angle of the lithium-ion battery separator prepared in Example 4. The electrolyte used for the contact angle test is a mixture of an electrolyte and a solvent. The electrolyte is LiPF6, the electrolyte concentration is 1 M, and the solvent is a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. By volume, the ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is 1:1:1.

[0091] Figure 3 is the cross-sectional scanning electron micrograph of the lithium-ion battery separator prepared in Comparative Example 6. Figure 4 is the cross-sectional scanning electron micrograph of the lithium-ion battery separator prepared in Example 4. From Figure 3 and Figure 4 it can be seen that after coating with the slurry containing hydrated aluminum silicate and porous alumina, the contact area between the coating and the surface of the base film increases, and the pore gaps decrease, so that the adhesion (peel strength) between the coating and the base film is further improved.

[0092] The needle-like hydrated aluminum silicate has good flexibility and a large specific surface area. It can tightly connect porous alumina particles together through physical entanglement, enhancing the adhesion between the coating and the base film. The hydrated aluminum silicate fills the pores and around the porous alumina, further optimizing the pore structure and electrolyte distribution of the separator, making the ionic conductivity further increase. At the same time, the framework network structure formed by their mutual interweaving supports each other in mechanical properties, greatly enhancing the overall strength and toughness of the separator. Porous alumina has a high melting point and a porous structure. The high melting point characteristic enables it to maintain a stable structure in a high-temperature environment, effectively improving the thermal stability of the separator. The linear needle-like structure of hydrated aluminum silicate plays a unique role in lithium-ion transport. Its needle-like morphology constructs additional lithium-ion transport channels inside the separator. These channels are intertwined with the original ion transport paths, giving lithium ions more path choices during the transport process, effectively avoiding the problem of uneven transport caused by too high or too low local ion concentration, and effectively inhibiting the growth of lithium dendrites (characterized by interface resistance. In the initial stage of lithium dendrite growth, the local contact of the interface may become poor, and the interface resistance may increase to a certain extent, while the interface resistance of the lithium-ion battery separator prepared in the example is much lower than that of the comparative example), which is beneficial to forming a uniform and dense lithium deposition layer, so that the transport distribution of lithium ions in the whole separator becomes more uniform and efficient, effectively ensuring the stable performance of the battery.

[0093] The above is an exemplary description of the present invention. It should be noted that without departing from the core of the present invention, any simple deformation, modification or equivalent replacement that can be made by those skilled in the art without creative labor falls within the protection scope of the present invention.

Claims

1. A lithium battery separator, characterized in that: include: The base film and the coating on the base film include porous alumina, hydrated aluminum silicate, ammonium polyacrylate and acrylate copolymer. The ratio of porous alumina, hydrated aluminum silicate, ammonium polyacrylate and acrylate copolymer is (10-20): (10-20): (0.2-0.5): (1-4) by mass.

2. The lithium battery separator according to claim 1, characterized in that: The hydrated aluminum silicate has a needle-like structure, and the length of the hydrated aluminum silicate is 5 to 20 μm, the width is 200 to 500 nm, and the thickness is 50 to 200 nm.

3. The lithium battery separator according to claim 1, characterized in that: The specific surface area of ​​porous alumina is 10 to 15 m 2 / g, pore size is 5-10nm.

4. A method for preparing a lithium battery separator, characterized in that: include: The slurry is coated on a base film and dried to form a coating on the base film to obtain a lithium battery separator, wherein the slurry includes: porous alumina, hydrated aluminum silicate, water, a dispersant and a binder, and the ratio of the porous alumina, hydrated aluminum silicate, water, the dispersant and the binder is (10-20): (10-20): (50-60): (0.2-0.5): (5-10) by mass.

5. A slurry, characterized in that: include: The porous alumina, hydrated aluminum silicate, water, dispersant and binder are present in a ratio of (10-20): (10-20): (50-60): (0.2-0.5): (5-10) by mass.

6. The slurry according to claim 5, characterized in that The dispersant is ammonium polyacrylate; the binder is an acrylate copolymer solution, and the content of the acrylate copolymer in the acrylate copolymer solution is 20-40wt%.

7. The slurry according to claim 5, characterized in that The particle size of the slurry is: D50 = 0.4-0.7 microns, D90 = 0.9-1.6 microns.

8. A method for preparing the slurry according to any one of claims 5 to 7, characterized in that: include: The porous alumina, hydrated aluminum silicate, water, a dispersant and a binder are mixed until uniform to obtain a slurry. The ratio of the porous alumina, hydrated aluminum silicate, water, a dispersant and a binder is (10-20): (10-20): (50-60): (0.2-0.5): (5-10) by mass.

9. Application of hydrated aluminum silicate and porous aluminum oxide to synergistically improve the liquid absorption rate, liquid retention rate, ionic conductivity, needle puncture strength and / or peel strength of the separator.

10. Application of hydrated aluminum silicate and porous alumina to synergistically reduce membrane shrinkage, interface resistance and / or contact angle.

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