Lithium nitrate sustained-release membrane as well as preparation method and application thereof

Abstract

The invention discloses a lithium nitrate sustained-release membrane as well as a preparation method and application thereof, and belongs to the technical field of sustained-release membranes. The preparation method comprises the following steps: uniformly mixing a lithium nitrate solution and a polyvinylidene fluoride-hexafluoropropylene copolymer solution, and preparing by adopting a tape casting method. The lithium nitrate is used as a raw material, the lithium nitrate and the polyvinylidene fluoride-hexafluoropropylene copolymer are prepared into the sustained-release membrane by adopting a tape casting method, the production process is simple, the cost is low, rapid forming can be achieved under the room temperature condition, the prepared sustained-release membrane can effectively protect Al foil and prevent Al corrosion, and the application effect is remarkable. The lithium nitrate is introduced into ethylene glycol dimethyl ether, so that the solubility of the lithium nitrate is maximized, a high-concentration lithium nitrate slow-release film is obtained, and the lithium nitrate slow-release film is applied to protection of Al corrosion, so that Al foil can be more effectively protected, and the performance stability of a Li-Al battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sustained-release membranes, and in particular to a lithium nitrate sustained-release membrane and a preparation method and application thereof. Background Art

[0002] Lithium nitrate is considered to be an excellent additive, NO3 - Able to enter Li + The formation of SEI film is regulated by the solvent structure. - The reduction products such as Li3N are excellent Li + Conductor, capable of accelerating Li + deposition / stripping behavior. Moreover, LiNO3 is usually used with other solvents or active substances to strengthen the SEI film and inhibit the growth of lithium dendrites. LiNO3 can decompose on the surface of lithium metal and further form a protective layer composed of inorganic / organic components, but because it reacts with the deposited lithium metal in each cycle, it is considered to be a "sacrificial electrolyte additive." This means that as long as there is LiNO3 salt in the electrolyte, the beneficial effect can be maintained, and once it is consumed, the electrochemical performance will deteriorate. However, the solubility of LiNO3 in ester electrolytes is very low, and it is worth studying to improve the solubility of LiNO3 in ester electrolytes.

[0003] The sustained-release membrane is a multifunctional layer composed of drugs, membrane materials and auxiliary components, which can continuously release drugs for a long time to achieve the effect of prolonging the drug's action time. The sustained-release membrane has the ability to reduce the drug release rate, improve the stability of the system, and increase the content of insoluble drugs. The application of LiNO3 to the sustained-release membrane can effectively solve the problem of LiNO3 being consumed during the cycle by continuously releasing LiNO3. However, the current LiNO3 sustained-release membrane has high cost, complex preparation process, low lithium nitrate concentration, poor protection effect on Al foil in Li-Al batteries, and insufficient electrochemical stability. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a lithium nitrate sustained-release membrane and a preparation method and application thereof, so as to solve the problems of high cost, complex preparation process, low solubility of lithium nitrate, poor protection effect on Al foil in Li-Al battery, and insufficient electrochemical stability of the existing LiNO3 sustained-release membrane.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] A method for preparing a lithium nitrate sustained-release film comprises the following steps:

[0007] The lithium nitrate solution and the polyvinylidene fluoride-hexafluoropropylene copolymer solution are uniformly mixed and prepared by a casting method.

[0008] Furthermore, the solvent of the lithium nitrate solution is ethylene glycol dimethyl ether or acetone.

[0009] Furthermore, the concentration of the lithium nitrate solution in ethylene glycol dimethyl ether is 0.25-0.3 g / mL; the concentration of the lithium nitrate solution in acetone is 0.01-0.05 g / mL.

[0010] Preferably, the concentration of the lithium nitrate solution in ethylene glycol dimethyl ether is 0.28 g / mL; the concentration of the lithium nitrate solution in acetone is 0.04 g / mL.

[0011] Furthermore, the solvent of the polyvinylidene fluoride-hexafluoropropylene copolymer solution is acetone, and the solution concentration is 0.01-0.1 g / mL.

[0012] Preferably, the solvent of the polyvinylidene fluoride-hexafluoropropylene copolymer solution is acetone, and the solution concentration is 0.08 g / mL.

[0013] Furthermore, the volume ratio of the lithium nitrate solution to the polyvinylidene fluoride-hexafluoropropylene copolymer solution is 0.8-1.2:0.8-1.2.

[0014] Preferably, the volume ratio of the lithium nitrate solution to the polyvinylidene fluoride-hexafluoropropylene copolymer solution is 1:1.

[0015] Furthermore, during mixing, the lithium nitrate solution needs to be poured into the polyvinylidene fluoride-hexafluoropropylene copolymer solution within 5 seconds and then mixed evenly.

[0016] A lithium nitrate sustained-release membrane is prepared by adopting the preparation method.

[0017] Application of the above lithium nitrate sustained-release film in preventing Al corrosion.

[0018] The present invention has the following beneficial effects:

[0019] (1) The present invention uses lithium nitrate as a raw material and prepares a sustained-release membrane by a casting method with a polyvinylidene fluoride-hexafluoropropylene copolymer. The production process is simple and the cost is low. It can be quickly formed at room temperature. The prepared sustained-release membrane can effectively protect Al foil and prevent Al corrosion, and the application effect is significant.

[0020] (2) The present invention uses ethylene glycol dimethyl ether to introduce lithium nitrate to maximize the solubility of lithium nitrate, and then mixes it with a polyvinylidene fluoride-hexafluoropropylene copolymer solution to prepare a sustained-release membrane, thereby obtaining a high-concentration lithium nitrate sustained-release membrane, which is applied to the protection of Al corrosion, can more effectively protect Al foil and improve the performance stability of Li-Al batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the LSV curve diagram in the test example;

[0022] Figure 2 This is the SEM surface morphology of the Al foil in the test example. DETAILED DESCRIPTION

[0023] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not used to limit the scope of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0024] Embodiment 1:

[0025] A method for preparing a high-concentration lithium nitrate sustained-release film comprises the following steps:

[0026] (1) Dissolve 2.8 g of lithium nitrate in 10 mL of ethylene glycol dimethyl ether at a dissolution temperature of 45° C. for 10 h to obtain reagent I; dissolve 0.8 g of polyvinylidene fluoride-hexafluoropropylene copolymer particles in 10 mL of acetone solution at a dissolution temperature of 60° C. to obtain solution II;

[0027] (2) Rapidly pour solution I into solution II (within 5 seconds) and mix thoroughly to obtain a casting solution;

[0028] (3) The casting liquid was cast onto a glass plate by a casting method, and then the cast film was immediately clamped by another glass plate and a glass plate as a substrate to reduce direct contact with moisture in the air. After forming, it was peeled off to obtain a high-concentration lithium nitrate sustained-release membrane, named 3.5:1LNO / PH.

[0029] Embodiment 2:

[0030] A method for preparing a high-concentration lithium nitrate sustained-release film comprises the following steps:

[0031] (1) Dissolve 2.5 g of lithium nitrate in 10 mL of ethylene glycol dimethyl ether at a dissolution temperature of 45° C. for 10 h to obtain reagent I; dissolve 0.5 g of polyvinylidene fluoride-hexafluoropropylene copolymer particles in 10 mL of acetone solution at a dissolution temperature of 60° C. to obtain solution II;

[0032] (2) Rapidly pour solution I into solution II (within 5 seconds) and mix thoroughly to obtain a casting solution;

[0033] (3) The casting liquid is cast onto a glass plate by a casting method, and then the cast film is immediately clamped by another glass plate and a glass plate as a substrate to reduce direct contact with moisture in the air. After forming, it is peeled off to obtain a high-concentration lithium nitrate sustained-release film.

[0034] Embodiment 3:

[0035] A method for preparing a high-concentration lithium nitrate sustained-release film comprises the following steps:

[0036] (1) 3.0 g of lithium nitrate was dissolved in 10 mL of ethylene glycol dimethyl ether at a dissolution temperature of 45° C. for 10 h to obtain reagent I; 1.0 g of polyvinylidene fluoride-hexafluoropropylene copolymer particles was dissolved in 10 mL of acetone solution at a dissolution temperature of 60° C. to obtain solution II;

[0037] (2) Rapidly pour solution I into solution II (within 5 seconds) and mix thoroughly to obtain a casting solution;

[0038] (3) The casting liquid is cast onto a glass plate by a casting method, and then the cast film is immediately clamped by another glass plate and a glass plate as a substrate to reduce direct contact with moisture in the air. After forming, it is peeled off to obtain a high-concentration lithium nitrate sustained-release film.

[0039] Embodiment 4:

[0040] A method for preparing a low-concentration lithium nitrate sustained-release film comprises the following steps:

[0041] (1) First, 0.8 g of lithium nitrate was dissolved in 20 mL of acetone at a dissolution temperature of 45° C., and then 0.8 g of polyvinylidene fluoride-hexafluoropropylene copolymer particles were added to the resulting solution at 60° C., and the mixture was fully dissolved and mixed to obtain a casting solution;

[0042] (2) The casting liquid was cast onto a glass plate by a casting method, and then the cast film was immediately clamped by another glass plate and a glass plate as a substrate to reduce direct contact with moisture in the air. After forming, it was peeled off to obtain a low-concentration lithium nitrate sustained-release membrane, named 1:1LNO / PH.

[0043] Comparative Example 1:

[0044] A method for preparing a sustained-release membrane without adding lithium nitrate comprises the following steps:

[0045] (1) dissolving 0.8 g of polyvinylidene fluoride-hexafluoropropylene copolymer particles in 20 mL of acetone solution at a dissolution temperature of 45° C. to prepare a casting solution;

[0046] (2) The casting liquid was cast onto a glass plate by a casting method, and then the cast film was immediately clamped by another glass plate and a glass plate as a substrate to reduce direct contact with moisture in the air. After molding, it was peeled off to obtain a sustained-release film, which was named Without LNO / PH.

[0047] Test example:

[0048] The slow-release films prepared in Example 1, Example 4 and Comparative Example 1 were applied to the assembly of Li-Al batteries. The prepared slow-release films were introduced into the positive electrode side of the battery and the voltage was 5 mV·s -1 The linear sweep voltammetry (LSV) test was carried out at a scan rate from open circuit voltage (OCV) to 6 V, and the SEM morphology of the Al foil was measured after the battery was operated at a constant voltage of 4.5 V for 6 h.

[0049] The experimental results are as follows Figure 1 and Figure 2 shown.

[0050] according to Figure 1 It can be seen that the Li-Al battery prepared in Comparative Example 1 increases with the increase of potential. When the potential is higher than 4V, the current gradually increases, indicating that the performance stability of the Li-Al battery decreases; while the low-concentration lithium nitrate sustained-release membrane prepared in Example 4 can effectively improve the stability of the Li-Al battery and increase the minimum potential at which the current changes. The high-concentration lithium nitrate sustained-release membrane prepared in Example 1 can significantly improve the stability of the Li-Al battery. The current hardly changes when the potential increases from 2V to 6V, which effectively protects the Al foil and has high performance stability.

[0051] according to Figure 2 It can be seen that the Al foil morphology of the Li-Al battery prepared in Comparative Example 1 changed significantly after being kept at a constant voltage of 4.5V for 6 hours, and a large number of cracks and pitting corrosion occurred, indicating that the Al corrosion was serious; the low-concentration lithium nitrate sustained-release film prepared in Example 4 provided a certain degree of protection for the Al foil. After working for 6 hours, only a small amount of pitting corrosion occurred, and the overall Al foil corrosion was good; the high-concentration lithium nitrate sustained-release film prepared in Example 1 provided effective protection for the Al foil. After working for 6 hours, the surface of the Al foil was still smooth and flat without any obvious defective structure.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a lithium nitrate sustained-release film, characterized in that: The following steps are involved: The lithium nitrate solution and the polyvinylidene fluoride-hexafluoropropylene copolymer solution are uniformly mixed and prepared by a casting method.

2. The method for preparing the lithium nitrate sustained-release film according to claim 1, characterized in that: The solvent of the lithium nitrate solution is ethylene glycol dimethyl ether or acetone.

3. The method for preparing the lithium nitrate sustained-release membrane according to claim 2, characterized in that: The concentration of the lithium nitrate solution in ethylene glycol dimethyl ether is 0.25-0.3 g / mL; the concentration of the lithium nitrate solution in acetone is 0.01-0.05 g / mL.

4. The method for preparing the lithium nitrate sustained-release film according to claim 1, characterized in that: The solvent of the polyvinylidene fluoride-hexafluoropropylene copolymer solution is acetone, and the solution concentration is 0.01-0.1 g / mL.

5. The method for preparing the lithium nitrate sustained-release film according to claim 1, characterized in that: The volume ratio of the lithium nitrate solution to the polyvinylidene fluoride-hexafluoropropylene copolymer solution is 0.8-1.2:0.8-1.

2.

6. The method for preparing the lithium nitrate sustained-release membrane according to claim 1, characterized in that: When mixing, the lithium nitrate solution needs to be poured into the polyvinylidene fluoride-hexafluoropropylene copolymer solution within 5 seconds and then mixed evenly.

7. A lithium nitrate sustained-release film, characterized in that: The method is prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the lithium nitrate sustained-release membrane according to claim 7 in preventing Al corrosion.

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