High-Safety Semi-Solid Electrolyte and Its Preparation Method, Lithium Battery

Abstract

The present invention discloses a highly safe semi-solid electrolyte, a preparation method thereof, and a lithium battery. The preparation method comprises: dissolving a fluorine-containing polymer and a perfluorosulfonic acid polymer solution in a solvent to obtain a mixed solution; coating the mixed solution on a substrate and drying it to obtain a composite film; and allowing the composite film to absorb an electrolyte to form a semi-solid electrolyte. The composite film can be prepared over a large area by coating, and then the composite film can be immersed in an electrolyte to obtain a semi-solid electrolyte. Therefore, the preparation method is simple, easy to industrialize, and can significantly reduce production costs. Due to electrostatic interaction, the electrolyte has an electrostatic attraction effect on lithium ions in the electrolyte and an electrostatic repulsion effect on anions in the electrolyte, thereby increasing the lithium ion migration number and reducing the anion migration number. The reduction in the anion migration number can prolong the nucleation time of lithium dendrites, thereby fundamentally inhibiting the nucleation and growth of lithium dendrites.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a highly safe semi-solid electrolyte and a preparation method thereof, and a lithium battery. Background Art

[0002] Currently, liquid electrolytes are the most widely used in lithium-ion batteries. However, these liquid electrolytes carry the risk of leakage and are prone to forming lithium dendrites on the electrode surfaces during battery cycling. The continued growth of these dendrites can pierce the separator, causing a short circuit between the positive and negative electrodes, which can easily lead to battery fires and explosions. Solid-state electrolytes play an important role in preventing lithium dendrites from penetrating the separator and causing a short circuit between the positive and negative electrodes. As a key component in improving lithium battery safety, solid-state electrolytes have garnered widespread attention. However, the low lithium ion conductivity of traditional solid-state electrolytes limits the battery's charge and discharge rate performance. Consequently, semi-solid electrolytes are attracting increasing attention.

[0003] However, existing technologies are complex to prepare semi-solid electrolytes, making them difficult to commercialize. They typically require specific conditions, such as vacuum reactors and high-temperature extraction, to produce composite separators and porous electrolytes, significantly increasing the complexity and production costs of the process. Furthermore, existing technologies primarily address the safety concerns associated with lithium dendrites by increasing the strength of the separator or electrolyte, failing to fundamentally suppress their nucleation and growth. Summary of the Invention

[0004] (1) Purpose of the invention

[0005] The purpose of the present invention is to provide a highly safe semi-solid electrolyte, a preparation method thereof, and a lithium battery. A composite film can be prepared over a large area by coating, and the composite film can be immersed in an electrolyte to obtain a semi-solid electrolyte. Therefore, the preparation method is simple and easy to industrialize, and the production cost can also be significantly reduced. The prepared semi-solid electrolyte has negative charge, can achieve ion selectivity, increase the lithium ion migration number, prolong the nucleation time of lithium dendrites, inhibit the nucleation and growth of lithium dendrites, and ensure the safety of the lithium battery.

[0006] (2) Technical solution

[0007] The first aspect of the present invention provides a method for preparing a highly safe semi-solid electrolyte, comprising: dissolving a fluorine-containing polymer and a perfluorosulfonic acid polymer solution in a solvent to obtain a mixed solution; coating the mixed solution on a substrate and drying it to obtain a composite film; and allowing the composite film to absorb an electrolyte to form a semi-solid electrolyte.

[0008] Furthermore, the perfluorosulfonic acid polymer solution includes Nafion solution; the fluorine-containing polymer includes polyvinylidene fluoride; and the solvent includes dimethylformamide.

[0009] Furthermore, the electrolyte includes a lithium salt and one or more of ethylene carbonate, propylene carbonate and dimethyl carbonate; wherein the lithium salt includes one or more of LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiN(CF3SO2)2.

[0010] Furthermore, the thickness of the film is 20 to 100 μm.

[0011] Furthermore, the composite film adsorbing the electrolyte to form a semi-solid electrolyte includes: immersing the composite film in the electrolyte to form a semi-solid electrolyte; wherein the immersion amount of the composite film is 2-5ul / cm 2 .

[0012] Furthermore, the fluorine-containing polymer and the perfluorosulfonic acid polymer solution are dissolved in a solvent to obtain a mixed solution comprising polyvinylidene fluoride, Nafion solution, and dimethylformamide in a mass ratio of 8-12:7.3-11.3:89-100.

[0013] Furthermore, the purity of the polyvinylidene fluoride is ≥99.0%, and the molecular weight of the polyvinylidene fluoride is about 40,000; the water content of the Nafion solution is ≤45%; and the purity of the dimethylformamide is ≥99.0%.

[0014] Furthermore, the mixed solution is coated on a substrate and dried to obtain a composite film, which includes: allowing the mixed solution to stand for a predetermined time and pouring it onto the surface of the substrate, placing the substrate with the mixed solution on a coating machine, adjusting the scraper scale to 20-100 μm, and performing scraping; placing the substrate coated with the mixed solution in a vacuum drying oven, adjusting the temperature to 50-60°C, and drying for more than 24 hours to obtain the composite film.

[0015] A second aspect of the present invention provides a highly safe semi-solid electrolyte prepared by the above-mentioned preparation method.

[0016] The third aspect of the present invention provides a lithium battery, comprising: a positive electrode, a negative electrode and the above-mentioned high-safety semi-solid electrolyte; wherein the fluorine atoms on the fluorine-containing polymer chain and the negative charges in the perfluorosulfonic acid polymer solution electrostatically attract the lithium ions in the electrolyte, so that each lithium ion is adsorbed on the fluorine atom; when charging and discharging, the adsorbed lithium ions shuttle back and forth between the positive electrode and the negative electrode under the action of the electric field force to achieve the migration of lithium ions; the fluorine atoms on the fluorine-containing polymer chain and the negative charges in the perfluorosulfonic acid polymer solution electrostatically repel the anions in the electrolyte, so that the number of anion migration is reduced, which can inhibit the nucleation of lithium dendrites.

[0017] Furthermore, the positive electrode includes any one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and ternary materials; the negative electrode includes carbon material, silicon material or lithium metal.

[0018] (3) Beneficial effects

[0019] The above technical solution of the present invention has the following beneficial technical effects:

[0020] 1. The technical solution of the present invention is to directly prepare a PVDF and Nafion composite film by coating, and then obtain a highly safe semi-solid electrolyte after soaking. Compared with existing PVDF solid electrolyte preparation methods, the preparation method is simple and easy to operate, and does not require a complex phase conversion process. The composite film can be prepared on a large area by coating, and then the composite film is immersed in an electrolyte to obtain a semi-solid electrolyte. Therefore, it is easy to industrialize and can significantly reduce production costs.

[0021] 2. Compared with solid electrolytes, semi-solid electrolytes have more free lithium ions, which can improve the lithium ion conductivity inside the battery and thus improve the battery rate performance. In addition, the semi-solid electrolyte prepared in the embodiment of the present invention has more negatively charged functional groups, which produce electrostatic attraction with lithium ions to achieve selective lithium ion transmission, increase the lithium ion migration number, reduce the anion migration number, prolong the lithium dendrite nucleation time, and fundamentally inhibit the growth of lithium dendrites, ensuring the intrinsic high safety of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a flow chart of a method for preparing a semi-solid electrolyte according to a first embodiment of the present invention;

[0023] Figure 2 is a flow chart of a method for preparing a semi-solid electrolyte according to a second embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of the transport structure of lithium ions on the PVDF chain;

[0025] Figure 4 Schematic diagram of the structure of semi-solid electrolyte inhibiting lithium dendrite growth.

[0026] Reference numerals:

[0027] 1-hydrogen atom, 2-carbon atom, 3-fluorine atom, 4-lithium ion, 5-positive electrode current collector, 6-positive electrode, 7-anion, 8-semi-solid electrolyte, 9-negative electrode, 10-negative electrode current collector. DETAILED DESCRIPTION

[0028] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0029] The first aspect of the present invention provides a method for preparing a highly safe semi-solid electrolyte, such as Figure 1 As shown, specifically including the following steps:

[0030] Step S10: dissolving the fluorinated polymer and the perfluorosulfonic acid polymer solution in a solvent to obtain a mixed solution. The fluorinated polymer is used as a base, and the perfluorosulfonic acid polymer solution is used as an additive. The mixture is dissolved in the solvent, mixed evenly, and allowed to stand for degassing to obtain a mixed solution.

[0031] In step S20, the mixed solution is coated on a substrate and dried to obtain a composite film. The drying process may be performed under a vacuum environment to obtain the composite film. The substrate may be a glass plate, which has a smooth surface and is easy to remove the dried composite film.

[0032] Step S30: Absorbing the electrolyte onto the composite film to form a semi-solid electrolyte. The composite film obtained after drying on the substrate can be completely immersed in the electrolyte, or the electrolyte can be evenly sprayed onto the composite film to allow the composite film to absorb the electrolyte, thereby forming a semi-solid electrolyte. In some embodiments, the electrolyte can include a lithium salt and an organic solvent, wherein the organic solvent is one or more of ethylene carbonate, propylene carbonate, and dimethyl carbonate. The prepared semi-solid electrolyte can include the composite film soaked in the electrolyte and the electrolyte.

[0033] In some embodiments, the perfluorosulfonic acid polymer solution includes a Nafion solution; the fluorinated polymer includes polyvinylidene fluoride (PVDF); and the solvent includes dimethylformamide (DMF).

[0034] In the embodiments of the present invention, a PVDF and Nafion composite film is directly prepared by coating, and then immersed in it to produce a highly safe semi-solid electrolyte. Compared with existing PVDF solid electrolyte preparation methods, this preparation method is simple and easy to operate, without requiring a complex phase conversion process. The composite film can be prepared over a large area by coating, and then immersed in an electrolyte to produce the semi-solid electrolyte. This makes industrialization easy and significantly reduces production costs. Compared to solid electrolytes, the semi-solid electrolyte prepared in the embodiments of the present invention has more free lithium ions, which can improve the lithium ion conductivity of the electrolyte. Furthermore, this semi-solid electrolyte can be used to prepare a lithium-ion battery. Due to electrostatic interactions, the lithium ions in the electrolyte electrostatically attract and repel anions in the electrolyte, thereby increasing the lithium ion transference number and reducing the anion transference number. This reduction in the anion transference number prolongs the nucleation time of lithium dendrites, thereby fundamentally suppressing the nucleation and growth of lithium dendrites and ensuring the inherent high safety of lithium-ion batteries. Therefore, the semi-solid electrolyte in the embodiments of the present invention has the effect of inhibiting lithium dendrites.

[0035] In some embodiments, the lithium salt in the electrolyte includes one or more of LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2.

[0036] In some embodiments, the composite film has a thickness of 20 to 100 μm.

[0037] In some embodiments, the process of forming a semi-solid electrolyte by adsorbing an electrolyte on the composite film comprises: immersing the composite film in an electrolyte to form a semi-solid electrolyte; wherein the immersion volume of the composite film is 2-5 ul / cm 2 For example, the immersion volume of the composite film can be 3-4ul / cm 2 The preparation process of directly immersing the composite film in the electrolyte is simple, easy to operate and industrialize, and can significantly reduce production costs.

[0038] In some embodiments, step S10 involves dissolving a fluorinated polymer and a perfluorosulfonic acid polymer solution in a solvent to obtain a mixed solution comprising polyvinylidene fluoride, Nafion solution, and dimethylformamide in a mass ratio of 8-12:7.3-11.3:89-100. In an exemplary embodiment, the mixture may be mixed in a ratio of polyvinylidene fluoride:Nafion solution:dimethylformamide = 0.1 g to 10 g:0.1 ml to 10 ml:1 ml to 50 ml.

[0039] In some embodiments, the purity of polyvinylidene fluoride is ≥99.0%; the molecular weight of polyvinylidene fluoride is approximately 40,000; the water content of the Nafion solution is ≤45%; and the purity of dimethylformamide is ≥99.0%.

[0040] In some embodiments, step S20, coating the mixed solution on a substrate and drying the mixed solution to obtain a composite film, comprises:

[0041] In step S21 , the mixed solution is allowed to stand for a predetermined time and poured onto the surface of the substrate. The substrate with the mixed solution is placed on a coating machine, and the scraper scale is adjusted to 20 to 100 μm for scraping.

[0042] In step S22 , the substrate coated with the mixed solution is placed in a vacuum drying oven, the temperature is adjusted to 50-60° C., and dried for more than 24 hours to obtain the composite film.

[0043] Composite films of different thicknesses can be obtained by adjusting the scraper scale on the coating machine, so the thickness of the prepared semi-solid electrolyte is controllable, the preparation method is simple, and easy to operate.

[0044] A second aspect of the present invention provides a semi-solid electrolyte prepared by the above-mentioned preparation method.

[0045] Lithium dendrite growth is a prominent issue currently affecting battery safety. Existing technologies typically address the separator and electrolyte, suppressing dendrite growth or penetration by increasing the strength of the separator or electrolyte, without addressing the root cause of the dendrite problem.

[0046] In order to solve the problem of lithium dendrites, the third aspect of the present invention provides a lithium battery, comprising: a positive electrode, a negative electrode and the above-mentioned semi-solid electrolyte; wherein the fluorine atoms on the fluorine-containing polymer chain and the negative charges in the perfluorosulfonic acid type polymer solution electrostatically attract the lithium ions in the electrolyte, so that each lithium ion is adsorbed on the fluorine atom; when charging and discharging, the adsorbed lithium ions shuttle back and forth between the positive electrode and the negative electrode under the action of the electric field force to achieve the migration of lithium ions; the fluorine atoms on the fluorine-containing polymer chain and the negative charges in the perfluorosulfonic acid type polymer solution electrostatically repel the anions in the electrolyte, so that the number of anion migration is reduced, which can inhibit the nucleation of lithium dendrites. In the embodiment of the present invention, the lithium battery may include a lithium ion battery, a lithium metal battery, and a lithium sulfur battery. The embodiment of the present invention solves the problem of lithium dendrite growth in lithium ion batteries by starting from the inhibition of lithium dendrite nucleation by the semi-solid electrolyte. When this semi-solid electrolyte is applied to a lithium-ion battery, due to electrostatic interaction, the lithium ions in the electrolyte have an electrostatic attraction effect, which electrostatically repels the anions in the electrolyte. This can increase the lithium ion transference number and reduce the anion transference number. The reduction in the anion transference number can prolong the nucleation time of lithium dendrites, thereby fundamentally inhibiting the nucleation and growth of lithium dendrites. Therefore, the semi-solid electrolyte in the embodiment of the present invention has the effect of inhibiting lithium dendrites.

[0047] In some embodiments, the positive electrode includes any one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and ternary materials; the negative electrode includes carbon material, silicon material, or lithium metal; for example, the negative electrode can be a graphite material.

[0048] Example 1: Preparation method of semi-solid electrolyte

[0049] like Figure 2 As shown, 1 g of PVDF and 1 ml of nafion were placed in a beaker. The Nafion additive was added here to increase the electronegativity of the electrolyte. 10 ml of N,N-dimethylformamide (DMF) was added and stirred for 24 hours, and then allowed to stand for 2 hours for degassing.

[0050] After the standing is completed, the mixed solution (slurry) is poured onto the surface of the glass plate, and the glass plate is placed on a coating machine with a scraper scale adjustable to 20 μm for scraping.

[0051] The glass plate coated with the mixed solution was placed in a vacuum drying oven and dried at 60° C. for 24 hours. The glass plate was taken out and the dried composite film was removed from the glass plate. The thickness of the composite film was 20 μm.

[0052] In the glove box, 10 ml of electrolyte was taken out with a beaker. The lithium salt was LiPF6 (the lithium salt of the electrolyte here is not limited to LiPF6, but can also be LiClO4, LiBF4, LiAsF6, etc.). The composite film was completely immersed in the electrolyte. The immersion volume of the composite film was 3.2 ul / cm 2 , and a semi-solid electrolyte is formed after the composite film is completely infiltrated.

[0053] Example 2: Assembling the semi-solid electrolyte into a lithium-ion battery

[0054] The semi-solid electrolyte obtained in Example 1 can be assembled into a lithium-ion battery, wherein the positive electrode material can be any one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and ternary materials, and the negative electrode material is graphite.

[0055] In the embodiment of the present invention, the semi-solid electrolyte can be prepared into a lithium-ion battery. More free lithium ions in the lithium salt can improve the lithium ion conductivity. The abundant electronegative functional groups of fluorine atoms (F) on PVDF and the abundant electronegative functional groups of SO3 on Nafion in the additive can improve the conductivity of lithium ions. - They can have an electrostatic attraction to lithium ions, so they can be adsorbed on the polymer chain. Then, due to the action of the electric field force during the charge and discharge process, they can promote the movement of the adsorbed lithium ions, thereby realizing the transmission of ions on the semi-solid electrolyte. Figure 3 As shown, the entire PVDF chain consists of hydrogen atom 1, carbon atom 2, and fluorine atom 3. The electronegative functional group fluorine atom 3 on the PVDF chain and SO3 in the additive Nafion - For the cations in the electrolyte, namely lithium ions (Li + )4 has an electrostatic attraction that can absorb lithium ions 4 in the electrolyte into the entire electrolyte, so that each lithium ion 4 is adsorbed on the fluorine atom 3 of the PVDF chain. Therefore, the lithium ions 4 are transported by the electrostatic effect of the semi-solid electrolyte and the electric field applied to the lithium ions, which can increase the number of lithium ions transferred.

[0056] In the embodiment of the present invention, the semi-solid electrolyte has ion selectivity, which can inhibit anion transport and prolong the nucleation time of lithium dendrites. The nucleation time of lithium dendrites can be calculated using the following formula:

[0057]

[0058] Where, t sand is the nucleation time of lithium dendrite; D app is the bipolar diffusion coefficient; Z0 is the charge number of the cation (Li+, Z0 = 1); C0 and J are the volume salt concentration and current density, respectively; F is the Faraday constant; t a It represents the migration number of anions and the migration number of lithium ions in the electrolyte (tLi+ ) is 1.

[0059] The semi-solid electrolyte in the embodiment of the present invention has more free lithium ions than the solid electrolyte because it is directly immersed in the lithium salt solution, thereby improving the conductivity of lithium ions. The rapid transmission of lithium ions can achieve high rate performance of the battery.

[0060] The semi-solid electrolyte in the embodiment of the present invention has an electrostatic attraction to lithium ions and an electrostatic repulsion to anions, such as Figure 4 As shown, the positive electrode current collector 5 and the positive electrode 6 are located on one side of the semi-solid electrolyte 8, and the negative electrode current collector 10 and the negative electrode 9 are located on the other side of the semi-solid electrolyte 8. When charging and discharging, the adsorbed lithium ions 4 will shuttle back and forth between the positive and negative electrodes under the action of the electric field force, that is, the migration of lithium ions is realized; when charging, the adsorbed lithium ions 4 will migrate from the positive electrode to the negative electrode under the action of the electric field force; when discharging, the adsorbed lithium ions 4 will migrate from the negative electrode to the positive electrode under the action of the electric field force; and the anions 7 can be blocked on the side of the semi-solid electrolyte 8 close to the positive electrode 6, which leads to a decrease in the migration number of the anions 7, as shown above. sand The reduction in the anion migration number shown in the formula can prolong the nucleation time of lithium dendrites, which further proves that the semi-solid electrolyte in the embodiment of the present invention can inhibit the nucleation of lithium dendrites and suppress lithium dendrites from the root.

[0061] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or illustrative of the principles of the present invention and do not constitute limitations of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention. In addition, the appended claims are intended to cover all variations and modifications that fall within the scope and metes and bounds of the appended claims, or equivalents thereof.

Claims

1. A method for preparing a highly safe semi-solid electrolyte, characterized in that: include: dissolving the fluorine-containing polymer and the perfluorosulfonic acid type polymer solution in a solvent to obtain a mixed solution; The mixed solution is coated on a substrate and dried to obtain a composite film having a thickness of 20 to 100 μm; The composite film is adsorbed with electrolyte to form a semi-solid electrolyte, comprising: immersing the composite film in electrolyte to form a semi-solid electrolyte; wherein the immersion amount of the composite film is 2-5ul / cm 2 .

2. The preparation method according to claim 1, characterized in that Perfluorosulfonic acid type polymer solutions include Nafion solutions; Fluoropolymers include polyvinylidene fluoride; Solvents include dimethylformamide.

3. The preparation method according to claim 1, characterized in that The electrolyte includes lithium salt and one or more of ethylene carbonate, propylene carbonate and dimethyl carbonate; wherein, The lithium salt includes one or more of LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2.

4. The preparation method according to claim 2, characterized in that The step of dissolving the fluorine-containing polymer and the perfluorosulfonic acid polymer solution in a solvent to obtain a mixed solution comprises: The mass ratio of polyvinylidene fluoride, Nafion solution and dimethylformamide is 8-12:7.3-11.3:89-100.

5. The preparation method according to claim 4, characterized in that The purity of polyvinylidene fluoride is ≥99.0%; The water content of the Nafion solution is ≤45%; The purity of the dimethylformamide is ≥99.0%.

6. The preparation method according to claim 1, characterized in that The mixed solution is coated on a substrate and dried to obtain a composite film, comprising: The mixed solution is allowed to stand for a predetermined time and poured onto the surface of the substrate. The substrate with the mixed solution is placed on a coating machine, and the scraper scale is adjusted to 20-100 μm for scraping. The substrate coated with the mixed solution is placed in a vacuum drying oven, the temperature is adjusted to 50-60° C., and dried for more than 24 hours to obtain the composite film.

7. A highly safe semi-solid electrolyte, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 6.

8. A lithium battery, characterized in that: include: A positive electrode, a negative electrode and a highly safe semi-solid electrolyte as claimed in claim 7; wherein, The fluorine atoms on the fluorine-containing polymer chain and the negative charges in the perfluorosulfonic acid polymer solution electrostatically attract the lithium ions in the electrolyte, so that each lithium ion is adsorbed on the fluorine atom; During charging and discharging, the adsorbed lithium ions shuttle back and forth between the positive electrode and the negative electrode under the action of the electric field force to achieve lithium ion migration; The fluorine atoms on the fluorine-containing polymer chain and the negative charges in the perfluorosulfonic acid polymer solution electrostatically repel the anions in the electrolyte, thereby reducing the anion migration number and inhibiting the nucleation of lithium dendrites.

9. The lithium battery according to claim 8, characterized in that The positive electrode includes any one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and ternary materials; The negative electrode includes carbon material, silicon material or lithium metal.

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