High heat-resistant high ionic conductivity lithium battery separator and preparation method thereof

Abstract

The application discloses a high-heat-resistance high-ionic-conductivity lithium battery diaphragm and a preparation method thereof. The high-heat-resistance high-ionic-conductivity lithium battery diaphragm comprises a base film and a coating layer on the base film, and the coating layer comprises porous alumina powder, a dispersing agent, an acrylic ester copolymer and a polyacrylamide copolymer. The particle size of the porous alumina powder is D10: 0.1-0.3 microns, D50: 0.3-0.5 microns and D90: 0.6-0.8 microns. The pore size of the porous alumina powder is 8-14 nm, and the specific surface area is 10-40 m 2 / g. In the application, the polyacrylamide is grafted on the porous alumina, and the diaphragm formed after coating on the surface of the base film is a porous composite diaphragm. The porous alumina improves the mechanical strength of the diaphragm, and the functional groups of the polyacrylamide serve as lithium-philic sites to form a fast channel for lithium ion transmission. The hairy polyacrylamide chain and the porous alumina cooperatively provide a channel for electrolyte diffusion, and can realize uniform distribution and rapid passing of lithium ions, thereby improving the long cycle efficiency of the lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically relating to a high heat-resistant and high ionic conductivity lithium battery separator and its preparation method. Background Technology

[0002] The separator plays a crucial role in batteries. In various battery systems, the separator primarily functions to separate the positive and negative electrodes, prevent short circuits, and allow ions to transport smoothly between them. However, separators currently face several pressing issues. One prominent challenge is low ionic conductivity. Since the separator's main function is ion transport, its ionic conductivity directly determines the speed of ion transport within the battery. Low ionic conductivity increases the battery's internal resistance, thereby reducing charge / discharge efficiency, power performance, and cycle life. Conversely, high ionic conductivity improves charge / discharge efficiency, significantly reduces charge / discharge time, more effectively disperses ions to ensure battery safety, reduces ion accumulation in the separator, and allows the battery to maintain a relatively stable capacity during multiple charge / discharge cycles. This avoids the problem of rapid capacity decay in certain areas due to poor ion transport, thus extending battery life. Therefore, increasing the ionic conductivity of the separator and addressing the issue of rapid battery capacity decay has become an important direction in current separator material research. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a lithium battery separator with high heat resistance and high ionic conductivity.

[0004] Another object of the present invention is to provide a method for preparing the above-mentioned high heat resistance and high ionic conductivity lithium battery separator.

[0005] The objective of this invention is achieved through the following technical solution.

[0006] A high heat-resistant and high ionic conductivity lithium battery separator includes: a base film and a coating on the base film. The coating includes: porous alumina powder, a dispersant, an acrylate copolymer and a polyacrylamide (PAM) copolymer. By mass parts, the ratio of porous alumina powder, dispersant, acrylate copolymer and polyacrylamide copolymer is (20-30):(0.2-0.5):(5-10):(0.5-4).

[0007] In the above technical solution, the dispersant is ammonium polyacrylate.

[0008] In the above technical solution, the particle size of the porous alumina powder is: D10: 0.1~0.3μm, D50: 0.3~0.5μm, D90: 0.6~0.8μm.

[0009] In the above technical solution, the porous alumina powder has a pore size of 8-14 nm and a specific surface area of ​​10-40 m². 2 / g.

[0010] In the above technical solution, the ratio of porous alumina powder, dispersant, acrylate copolymer and polyacrylamide copolymer by mass parts is (20-25):(0.2-0.5):(5-8):(2-4).

[0011] The above-mentioned method for preparing a high heat-resistant and high ionic conductivity lithium battery separator includes: coating a coating slurry onto a base film, drying it, and obtaining a coating layer on the base film to obtain a high heat-resistant and high ionic conductivity lithium battery separator. The coating slurry includes: water, porous alumina powder, dispersant, acrylate copolymer and polyacrylamide copolymer.

[0012] In the above technical solution, the coating speed is 20-40 m / min.

[0013] In the above technical solution, the thickness of the coating is 2 to 3 micrometers.

[0014] In the above technical solution, the drying temperature is 30-70℃ and the drying time is 1-5 minutes.

[0015] A coating slurry includes: water, porous alumina powder, dispersant, binder, and additive, wherein the binder is an acrylate copolymer solution, and the additive is a polyacrylamide copolymer solution. By mass parts, the ratio of the acrylate copolymer in the water, porous alumina powder, dispersant, and binder to the polyacrylamide copolymer in the additive is (60-80):(20-30):(0.2-0.5):(5-10):(0.5-4).

[0016] In the above technical solution, the content of acrylate copolymer in the acrylate copolymer solution is 60-80 wt%.

[0017] In the above technical solution, the content of polyacrylamide copolymer in the polyacrylamide copolymer solution is 10-20 wt%.

[0018] In the above technical solution, the ratio of the water, porous alumina powder, dispersant, binder acrylate copolymer and additive polyacrylamide copolymer, by mass parts, is (60-80):(20-25):(0.2-0.5):(5-8):(2-4).

[0019] The method for preparing the above-mentioned coating slurry includes: mixing water, porous alumina powder, dispersant, binder and additives until uniform to obtain the coating slurry.

[0020] The method for preparing the above-mentioned coating slurry is as follows: water, dispersant and porous alumina powder are mixed until uniform to obtain a first solution, and the first solution, binder and additives are mixed until uniform to obtain the coating slurry.

[0021] In the above technical solution, water, dispersant and porous alumina powder are mixed and stirred at a rotation speed of 1400-2500 r / min and a revolution speed of 40-60 r / min for 15-25 minutes until uniform, to obtain the first solution.

[0022] In the above technical solution, the first solution, binder and additive are mixed and simultaneously ultrasonicated and stirred in a vacuum environment for 15 to 25 minutes until uniform, to obtain the coating slurry. The vacuum pressure of the vacuum environment is 130 to 1300 Pa, the ultrasonic frequency is 5 to 8 kHz, the rotation speed of the stirring is 1200 to 4000 r / min and the revolution speed is 30 to 50 r / min.

[0023] In the above technical solution, the particle size of the coating slurry is: D50: 0.350~0.500 micrometers, D90: 0.910~1.200 micrometers.

[0024] Applications of polyacrylamide (PAM) and porous alumina in synergistic improvement of membrane ionic conductivity, air permeability, heat resistance, wettability, and needle penetration strength.

[0025] Application of polyacrylamide (PAM) and porous alumina to synergistically improve battery capacity retention.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] This invention employs polyacrylamide (PAM) grafted onto porous alumina (physical grafting). The resulting membrane, after being coated onto the base film surface, is a porous composite membrane. The porous alumina enhances the mechanical strength of the membrane, while the functional groups of the polyacrylamide, acting as lithiophilic sites, form rapid channels for lithium-ion transport. The efficient adhesion and uniform distribution of the porous composite membrane at the molecular level provide a high concentration of functional sites, achieving a uniform and rapid lithium-ion flux at the molecular level on the electrode surface, thereby improving the membrane's ionic conductivity, thermal stability, and mechanical strength. The hairy polyacrylamide chains (PAM chains) and porous alumina synergistically provide channels for electrolyte diffusion, enabling uniform lithium-ion distribution and rapid passage, thus improving the long-cycle efficiency (capacity retention) of the lithium-ion battery. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of lithium-ion deposition during the charging process of the battery prepared in Comparative Example 5.

[0029] Figure 2This is a schematic diagram of lithium-ion deposition during the charging process of the battery prepared in Example 4;

[0030] Figure 3 This is a schematic diagram of polyacrylamide (PAM) grafted onto porous alumina. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0032] Polyacrylamide copolymer solution: Henan Guyuan Environmental Protection Technology Co., Ltd., number average molecular weight is 100-300 million Da;

[0033] Acrylic copolymer solution: Ningbo Xinfei Plastics Co., Ltd., number average molecular weight 500,000-800,000 Da;

[0034] Ammonium polyacrylate: Shanghai Sanrui Polymer Materials Technology Co., Ltd.

[0035] Porous alumina powder:

[0036]

[0037]

[0038] Dual planetary mixer: XFZH-30L.

[0039] In the following examples, the water used is pure water.

[0040] In the following examples, the base film is a PE film (7 μm thick).

[0041] In the following embodiments, the electrolyte is a mixture of electrolyte and solvent, the electrolyte is lithium hexafluorophosphate (LiPF6), and the solvent is a mixture of ethylene carbonate, propylene carbonate and dimethyl carbonate. The concentration of the electrolyte in the electrolyte is 1.0M, and the ratio of ethylene carbonate, propylene carbonate and dimethyl carbonate by volume is 1:1:1.

[0042] Ionic conductivity: The test temperature was 25℃ and the relative humidity was 30%.

[0043] Examples 1-3

[0044] A method for preparing a coating slurry includes: mixing water, a dispersant, and porous alumina powder; stirring the mixture in a double planetary mixer at a rotation speed of 2500 r / min and a revolution speed of 40 r / min for 15 minutes until homogeneous, obtaining a first solution; mixing the first solution, a binder, and an additive; and simultaneously ultrasonicating and stirring the mixture in a double planetary mixer in a vacuum environment with high dispersion ultrasonic oscillation characteristics for 20 minutes until homogeneous (vacuum pressure is 1000 Pa, ultrasonic frequency is 5 kHz, rotation speed is 1300 r / min, and revolution speed is 40 r / min). n), to obtain a coating slurry, the binder being an acrylate copolymer solution (the acrylate copolymer is a copolymer of acrylate and vinylidene fluoride), the additive being a polyacrylamide copolymer solution (the polyacrylamide copolymer is a copolymer of acrylamide and acrylic acid), and the dispersant being ammonium polyacrylate. The ratio of the acrylate copolymer in water, porous alumina powder, dispersant, binder, and additive to the polyacrylamide copolymer is X by mass. The content of the acrylate copolymer in the acrylate copolymer solution is 70 wt%, and the content of the polyacrylamide copolymer in the polyacrylamide copolymer solution is 15 wt%. The value of X is shown in Table 1.

[0045] Table 1

[0046] Coating slurry X Example 1 67：23:0.5:8:1.5 Example 2 67：23:0.5:6:3.5 Example 3 69：21:0.5:6:3.5

[0047] The particle size of the coating slurry prepared in Example 1 is: D50: 0.468 μm, D90: 1.068 μm; the particle size of the coating slurry prepared in Example 2 is: D50: 0.435 μm, D90: 1.057 μm; the particle size of the coating slurry prepared in Example 3 is: D50: 0.433 μm, D90: 1.135 μm.

[0048] Comparative Example 1

[0049] A method for preparing a coating slurry includes: mixing water, a dispersant, and porous alumina powder; stirring in a double planetary mixer at a rotation speed of 2500 r / min and a revolution speed of 40 r / min for 25 minutes; then sonicating at a frequency of 5 kHz for 15 minutes to obtain solution A; mixing solution A with a binder; and simultaneously sonicating and stirring in a double planetary mixer with a vacuum environment that simultaneously has high dispersion ultrasonic oscillation characteristics for 15 minutes until homogeneous (vacuum pressure is 1000 Pa, ultrasonic frequency is 5 kHz, rotation speed is 1500 r / min, and revolution speed is 40 r / min) to obtain the coating slurry. The binder is an acrylate copolymer solution (the acrylate copolymer is a copolymer of acrylate and vinylidene fluoride), and the dispersant is ammonium polyacrylate. By mass, the ratio of water, porous alumina powder, dispersant, and binder to the acrylate copolymer is 64:30:0.5:3.5, and the content of the acrylate copolymer in the acrylate copolymer solution is 70 wt%.

[0050] Comparative Example 2

[0051] A method for preparing a coating slurry includes: mixing water, a dispersant, and conventional alumina powder; stirring in a double planetary mixer at a rotation speed of 2500 r / min and a revolution speed of 40 r / min for 25 minutes; then sonicating at a frequency of 5 kHz for 15 minutes to obtain solution B; mixing solution B with a binder; and simultaneously sonicating and stirring in a double planetary mixer with a vacuum environment that simultaneously possesses high dispersion ultrasonic oscillation characteristics for 20 minutes until homogeneous (vacuum pressure is 1000 a, ultrasonic frequency is 5 kHz, rotation speed is 1500 r / min, and revolution speed is 40 r / min) to obtain the coating slurry. The binder is an acrylate copolymer solution (the acrylate copolymer is a copolymer of acrylate and vinylidene fluoride), and the dispersant is ammonium polyacrylate. By mass, the ratio of water, conventional alumina powder, dispersant, and binder to the acrylate copolymer is 64:30:0.5:3.5, and the content of the acrylate copolymer in the acrylate copolymer solution is 70 wt%. The particle sizes of conventional alumina powder are D10: 0.325 μm, D50: 0.519 μm, and D90: 1.054 μm, with a specific surface area of ​​15.4 m². 2 / g, with a pore size of 8.5nm.

[0052] Comparative Example 3

[0053] A method for preparing a coating slurry is basically the same as that in Example 1, except that "porous alumina powder" is replaced with "conventional alumina powder of Comparative Example 2".

[0054] Examples 4-6 and Comparative Examples 4-6

[0055] A battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode, negative electrode, electrolyte, and separator are packaged to obtain a soft-pack battery with an area of ​​10cm × 10cm and a thickness of 3mm. The positive electrode is prepared by drying lithium iron phosphate powder to remove moisture, followed by drying in an oven at 100℃ for 24 hours. The negative electrode is prepared by drying graphite in an oven at 100℃ for 24 hours to remove impurities and moisture from the graphite surface. The separator is prepared by placing a base film on a coating machine, coating one side of the base film with a coating slurry (coating speed Y m / min), and then guiding it into a drying device (oven) under the traction of a traction roller, drying at 35℃ for 3 minutes to obtain a coating on the base film, thus obtaining the separator. The coating slurry is one of Examples 1-3 and Comparative Examples 1-3.

[0056] Table 2

[0057] Battery Y(m / min) The coating slurry used to prepare the diaphragm Example 4 20 Example 1 Example 5 20 Example 2 Example 6 20 Example 3 Comparative Example 4 20 Comparative Example 1 Comparative Example 5 30 Comparative Example 2 Comparative Example 6 20 Comparative Example 3

[0058] The test data for the diaphragm prepared in Example 4 are as follows:

[0059]

[0060]

[0061] The test data for the diaphragm prepared in Example 5 are as follows:

[0062]

[0063] The test data for the diaphragm prepared in Example 6 are as follows:

[0064]

[0065] The test data for the diaphragm prepared in Comparative Example 4 are as follows:

[0066]

[0067] The test data of the lithium battery separator prepared in Comparative Example 5 are as follows:

[0068]

[0069] The test data of the lithium battery separator prepared in Comparative Example 6 are as follows:

[0070]

[0071]

[0072] At a current density of 0.3C, the battery prepared in Example 4 retained 90.2% of its capacity after 500 cycles, the battery prepared in Example 5 retained 91.3% of its capacity after 500 cycles, the battery prepared in Example 6 retained 90.8% of its capacity after 500 cycles, the battery prepared in Comparative Example 4 retained 83.3% of its capacity after 500 cycles, the battery prepared in Comparative Example 5 retained 81.2% of its capacity after 500 cycles, and the battery prepared in Comparative Example 6 retained 82.5% of its capacity after 500 cycles.

[0073] Figure 1 This is a schematic diagram of lithium-ion deposition during the charging process of the battery prepared in Comparative Example 5. The current collector is used to efficiently collect Li ions near the negative electrode and concentrate them into a larger current. During charging, Li ions gradually attach to the surface of the current collector (uneven distribution). During the Li ion deposition process, the electrode surface inevitably becomes microscopically rough, and the electric field near the electrode surface is uneven. During battery operation, Li ions preferentially attach to the surface with a stronger electric field in the current collector, gradually forming a pointed ionization layer. Figure 1 In the middle ("SEI"), Li dendrites are formed. The generated Li dendrites can bridge the space between electrodes, thereby creating the battery circuit.

[0074] Figure 2 This diagram illustrates lithium-ion deposition during the charging process of the battery prepared in Example 4 of this invention. During charging, PAM is interspersed within alumina. Since PAM is a hairy chain with polar groups, its surface includes C=O and NH bonds. The hairy chain with polar groups provides a high concentration of functional groups and abundant functional sites, enabling effective adhesion and uniform distribution of lithium ions. During Li-ion deposition, the electric field near the electrode surface is uniform. Simultaneously, the rapid diffusion channels formed between PAM and porous alumina molecules allow Li ions to quickly and uniformly adhere to the current collector surface, achieving dendrite-free uniform lithium-ion deposition at very high current densities, thereby ensuring the thermal stability of the coating membrane and the safety of the battery. Furthermore, the gaps between the stacked PAM and porous alumina molecules provide rapid diffusion channels for the electrolyte, accelerating lithium-ion transport and thus improving battery charging and discharging efficiency.

[0075] Figure 3 This is a schematic diagram of polyacrylamide (PAM) grafted onto porous alumina. Figure 3 It can be seen that polyacrylamide (PAM) is used to modify the surface of porous alumina, and the PAM with hairy chains is successfully grafted onto the porous alumina to form a porous composite membrane.

[0076] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A lithium battery separator with high heat resistance and high ionic conductivity, characterized in that, include: The base film and the coating on the base film, the coating comprising: porous alumina powder, dispersant, acrylate copolymer and polyacrylamide copolymer, wherein the ratio of porous alumina powder, dispersant, acrylate copolymer and polyacrylamide copolymer by mass parts is (20~30):(0.2~0.5):(5~10):(0.5~4); the acrylate copolymer is a copolymer of acrylate and vinylidene fluoride; the functional groups of polyacrylamide serve as lithiophilic sites, forming fast channels for lithium-ion transport; the polyacrylamide copolymer is a copolymer of acrylamide and acrylic acid, wherein the pore size of the porous alumina powder is 8~14 nm and the specific surface area is 10~40 m². 2 / g, the particle size of the porous alumina powder is: D10: 0.1~0.3μm, D50: 0.3~0.5μm, D90: 0.6~0.8μm.

2. The method for preparing a high heat-resistant and high ionic conductivity lithium battery separator as described in claim 1, characterized in that, include: A coating slurry is applied to a base film and dried to obtain a coating layer on the base film, resulting in a high heat-resistant and high ionic conductivity lithium battery separator. The coating slurry includes: water, porous alumina powder, dispersant, acrylate copolymer and polyacrylamide copolymer.

3. The preparation method according to claim 2, characterized in that, The coating slurry comprises: water, porous alumina powder, dispersant, binder and additive, wherein the binder is an acrylate copolymer solution and the additive is a polyacrylamide copolymer solution. By mass parts, the ratio of the acrylate copolymer in the water, porous alumina powder, dispersant and binder to the polyacrylamide copolymer in the additive is (60~80):(20~30):(0.2~0.5):(5~10):(0.5~4).

4. The preparation method according to claim 3, characterized in that, The acrylate copolymer solution contains 60-80 wt% acrylate copolymer; the polyacrylamide copolymer solution contains 10-20 wt% polyacrylamide copolymer.

5. The preparation method according to claim 4, characterized in that, The particle size of the coating slurry is: D50: 0.350~0.500 micrometers, D90: 0.910~1.200 micrometers.

6. The preparation method according to claim 5, characterized in that, The method for preparing the coating slurry includes: mixing water, porous alumina powder, dispersant, binder and additives until uniform to obtain the coating slurry.

Images