Process for the preparation and use of liquid crystalline electrolytes based on polymerizable ionic liquids

Abstract

The application discloses a preparation method and application of a liquid crystal state electrolyte based on a polymerizable ionic liquid, and a base of the prepared liquid crystal state electrolyte is a polymerizable ionic liquid and a liquid crystal elastomer; the polymer network is also filled with lithium salt and ionic liquid, can further provide a large amount of free lithium ions for the system, and further promotes the transmission of lithium ions; and after being polymerized into a film by ultraviolet, the safety hidden troubles such as leakage and explosion existing in traditional liquid state electrolytes can be further reduced; the film formation is carried out by using liquid crystal boxes with different sizes, the electrolyte film thickness can be adjusted, and different responses to different requirements can be realized. The liquid crystal state electrolyte prepared by the method has stable structure, high ion conductivity, a wide electrochemical window and superior cycle rate performance.

Description

Technical Field

[0001] This invention belongs to the field of conductive dielectric energy storage material preparation technology, specifically relating to a preparation method and application of a liquid crystal electrolyte based on polymerizable ionic liquid. Background Technology

[0002] With the widespread application of renewable energy sources such as solar and wind power, advancements in energy storage technology have become crucial. The increasing demand for portable electronic devices, electric vehicles, and large-scale advanced energy storage has also spurred exploration of higher-performance energy storage devices. Lithium-ion batteries, as both energy storage devices and power sources, have become one of the most important rechargeable battery technologies today. The electrolyte is a vital component of lithium batteries, crucial for improving their electrochemical performance and safety. However, the organic liquid electrolytes used in traditional lithium-ion batteries pose a series of serious safety hazards, including decomposition, leakage, spontaneous combustion, and even explosion. Solid electrolytes, due to their high safety and excellent electrochemical performance, have become a research hotspot for replacing liquid electrolytes. Solid electrolytes possess advantages such as non-volatility, high-temperature resistance, non-corrosiveness, non-explosiveness, and significantly reduced reactivity with lithium metal.

[0003] In recent years, liquid crystal electrolytes have attracted widespread attention as an emerging energy material. Liquid crystals are a state of matter with properties between traditional liquids and solid crystals, possessing both the fluidity of liquids and the anisotropy of solids, and have wide applications in optoelectronics, display technology, and sensors. Since the 1990s, the transport of lithium ions in liquid crystals has been reported. The anisotropy of liquid crystals allows them to form nanoscale segregated structures through self-assembly, providing ordered transport channels for lithium ions and thus affecting the electrochemical performance of batteries. In addition, when liquid crystal materials are used as electrolytes, they also generate sufficient anchoring strength and moderate highest occupied molecular orbitals (HOMOs), which can effectively suppress the formation of lithium dendrites and improve the interfacial stability of batteries.

[0004] Liquid crystal elastomers (LCEs) are liquid crystal polymers that, after appropriate cross-linking, exhibit elasticity in an isotropic or liquid crystal state, combining the properties of both liquid crystals and elastomers. They can deform in response to external stimuli (such as electric fields, temperature, and pressure) and even return to their original shape. This characteristic allows LCEs to maintain good stability and adaptability under various mechanical environments. LCEs are typically composed of alternating polymer segments and liquid crystal molecules, a structure that provides a favorable environment for ion transport. Liquid crystal molecules can form an ordered arrangement, potentially improving the ionic conductivity of electrolytes. The modulation of the liquid crystal structure can also optimize the ion channel network to some extent, increasing ion mobility and thus improving the conductivity of electrolytes. The addition of suitable salts or ionic liquids can effectively enhance the ionic conductivity of some LCEs. However, significant challenges remain in achieving breakthroughs in the performance and application of liquid crystal materials in the electrolyte field. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for preparing and applying a liquid crystal electrolyte based on a polymerizable ionic liquid. The preparation method of this invention is low-cost, high-yield, simple in process, and easy to control in reaction. Furthermore, the electrolyte prepared according to this method exhibits strong conductivity and excellent electrochemical performance when applied to lithium-ion batteries.

[0006] To achieve the above objectives, the present invention provides the following technical solution.

[0007] The first aspect of this invention provides a method for preparing a liquid crystal electrolyte based on a polymerizable ionic liquid, comprising the following steps:

[0008] S1: Lithium bis(trifluoromethanesulfonyl)imide was added to 1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imide and ultrasonically dispersed until completely dissolved to obtain solution A;

[0009] S2: Mix 2-methyl-1,4-phenylenebis(4-(3-(acryloyloxy)propoxy)benzoate) and 1-vinyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imine salt in a molar ratio of 3:1 to 1:1, heat until completely dissolved, and stir thoroughly to obtain solution B;

[0010] S3: Add the photoinitiator 1-hydroxycyclohexylphenyl ketone to 2,2'-(ethylenedioxy)diethylthiol and ultrasonically disperse until completely dissolved to obtain solution C;

[0011] S4: Add the obtained solution B dropwise to solution A and stir until homogeneous to obtain mixed solution D; add solution C to mixed solution D and stir thoroughly, then sonicate until uniformly dispersed to obtain solution E; slowly draw solution E into a liquid crystal cell of constant thickness, polymerize it fully under ultraviolet light, and then vacuum dry it to obtain the final product, liquid crystal electrolyte.

[0012] Furthermore, in solution A, the mass fraction of lithium bis(trifluoromethanesulfonylimide) is 5–8%.

[0013] Furthermore, in solution C, 1-hydroxycyclohexyl benzophenone is added to a mass fraction of 5–20% of 2,2'-(ethylenedioxy)diethylthiol.

[0014] Furthermore, the ultrasonic dispersion time in steps S1, S3, and S4 is 10–20 min.

[0015] Furthermore, the stirring described in steps S2 and S4 is carried out using a magnetic stirrer at a speed of 500–700 r / min for a duration of 5–10 min.

[0016] Furthermore, the vacuum drying described in step S4 is carried out at 80°C for 8–12 hours.

[0017] Furthermore, the intensity of the ultraviolet light in step S4 is 100–120 mw / cm². 2 .

[0018] A second aspect of the present invention provides a liquid crystal electrolyte based on a polymerizable ionic liquid, which is prepared by the above-described method for preparing a liquid crystal electrolyte based on a polymerizable ionic liquid.

[0019] The third aspect of the present invention provides the application of the liquid crystal electrolyte based on polymerizable ionic liquid in lithium-ion batteries.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) This invention designs and regulates the mechanical and electrochemical properties of the product by controlling important parameters such as the amount and type of raw materials added, the ratio of carbon-carbon double bonds to mercapto groups, polymerization temperature, and polymerization time. It successfully prepares a liquid crystal electrolyte that combines mechanical strength and stable cycling. The preparation method is efficient, the preparation process is simple, the reaction process is easy to control, and it is suitable for large-scale production.

[0022] (2) This invention designs a liquid crystal electrolyte based on polymerizable ionic liquids. The liquid crystal material can self-assemble to form multidimensional ion transport channels, which is beneficial to improving the efficiency of ion transport. Liquid crystal elastomers refer to non-crosslinked liquid crystal polymers that are moderately crosslinked and exhibit elasticity in an isotropic or liquid crystal state. Liquid crystal elastomers combine the anisotropy of liquid crystals with the rubber elasticity of polymer networks. The liquid crystal monomer 2-methyl-1,4-phenylene bis(4-(3-(acryloyloxy)propoxy)benzoate) (RM257) used in this invention has a rod-like structure with a length ratio of 4:1, and the molecules are systematically arranged due to the presence of polar and polarizing groups at the molecular ends. Excessive mesocrystalline units can cause the polymer film to be too stiff. The introduction of dithiol to prepare liquid crystal elastomers through the click reaction of double bonds to thiol groups reduces the stiffness of the system and increases the mechanical strength of the solid polymer film while maintaining the original electrochemical performance, greatly enhancing its feasibility.

[0023] (3) The present invention introduces polymerizable ionic liquid on the basis of liquid crystal elastomer and further combines it with network structure to form polymer structure. The polyionic liquid contains imidazole groups, which can promote the transport of lithium ions.

[0024] (4) The liquid crystal electrolyte prepared in this invention is applied to a lithium-ion battery with lithium iron phosphate as the positive electrode. Testing shows that it exhibits good electrochemical performance. Among alkali metal ion batteries, lithium-ion batteries have significant advantages, mainly due to: first, lithium-ion batteries can store more energy, are small in size and light in weight, making them very suitable for mobile devices and electric vehicles; second, lithium-ion batteries have a long cycle life, with more charge-discharge cycles compared to other batteries, typically reaching hundreds to thousands of cycles; and third, lithium-ion batteries use fewer harmful substances and have a higher recycling rate compared to traditional batteries such as lead-acid batteries. The use of this polymer as a lithium-ion electrolyte material is of great research significance for exploring and improving the electrochemical performance of liquid crystal polymer electrolytes. Attached Figure Description

[0025] Figure 1 This is the X-ray diffraction pattern of the liquid crystal electrolyte prepared in Example 1 of this invention;

[0026] Figure 2 This is a 5kx magnified image of the liquid crystal electrolyte prepared in Example 1 of this invention under a scanning electron microscope;

[0027] Figure 3 This is a cross-sectional image of the liquid crystal electrolyte prepared in Example 1 of this invention under a scanning electron microscope;

[0028] Figure 4 This describes the lithium electroplating stripping performance of the liquid crystal electrolyte prepared in Example 1 of this invention under different current densities.

[0029] Figure 5 This is a rate performance diagram of the liquid crystal electrolyte prepared in Example 1 of the present invention as a lithium-ion battery electrolyte.

[0030] Figure 6 This is a cycle performance diagram of the liquid crystal electrolyte prepared in Example 1 of the present invention as an electrolyte for a lithium-ion battery.

[0031] Figure 7 This is a cycle performance diagram of the liquid crystal electrolyte prepared in Example 2 of the present invention as an electrolyte for a lithium-ion battery. Detailed Implementation

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0033] Example 1: A method for preparing a liquid crystal electrolyte based on polymerizable ionic liquids, comprising the following steps:

[0034] S1: Add lithium bis(trifluoromethanesulfonyl)imide to 1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imide and sonicate for 10 min until completely dissolved to obtain solution A with a lithium salt mass fraction of 6.25%;

[0035] S2: Mix 2-methyl-1,4-phenylenebis(4-(3-(acryloyloxy)propoxy)benzoate) and 1-vinyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imine salt in a molar ratio of 3:1, heat under a blower for 5 minutes until completely dissolved, and then stir thoroughly to obtain solution B;

[0036] S3: Add the photoinitiator 1-hydroxycyclohexylphenyl ketone to 2,2'-(ethylenedioxy)diethylthiol and sonicate for 10 min until completely dissolved to obtain a solution C with a photoinitiator mass fraction of 3.95%;

[0037] S4: Add solution B dropwise to solution A and stir magnetically at 500 r / min for 10 min to obtain a homogeneous mixed solution D; slowly add solution C to mixed solution D and stir thoroughly, then sonicate for 10 min until uniformly dispersed to obtain solution E; slowly draw solution E into a liquid crystal cell of constant thickness using a capillary tube, polymerize it thoroughly under ultraviolet light for 10 min, and then vacuum dry to obtain liquid crystal polymer electrolyte (LCPE).

[0038] The LCPE prepared in Example 1 was analyzed using X-ray diffraction. The results are shown in [reference needed]. Figure 1 .Depend on Figure 1As can be seen, the obtained LCPE exhibits a characteristic peak at 20°.

[0039] The LCPE1 prepared in Example 1 was observed using a field emission scanning electron microscope. The results are shown in [reference needed]. Figure 2 , Figure 3 It can be seen that its surface forms a complex network of wrinkles, which is conducive to the transport of lithium ions, and its thickness is maintained at 200μm.

[0040] When the LCPE1 prepared in Example 1 was used as a lithium-ion battery electrolyte, its cycle performance was tested at a current density of 1C. The results are shown in [reference needed]. Figures 4 to 6 The battery, after 300 electrochemical cycles at a relatively high current density of 1C, still maintains a specific capacity close to 80 mAh g. -1 The coulombic efficiency is 92.3%, indicating that the electrode has good cycle stability and high lithium storage capacity, demonstrating excellent electrochemical performance.

[0041] Example 2: A method for preparing a liquid crystal electrolyte based on polymerizable ionic liquids, comprising the following steps:

[0042] S1: Add lithium bis(trifluoromethanesulfonyl)imide to 1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imide and sonicate for 10 min until completely dissolved to obtain solution A with a lithium salt mass fraction of 6.25%;

[0043] S2: Mix 2-methyl-1,4-phenylenebis(4-(3-(acryloyloxy)propoxy)benzoate) and 1-vinyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt in a 1:1 molar mass ratio, heat under a blower for 5 min until completely dissolved, and then stir thoroughly to obtain solution B;

[0044] S3: Add the photoinitiator 1-hydroxycyclohexylphenyl ketone to 2,2'-(ethylenedioxy)diethylthiol and sonicate for 10 min until completely dissolved to obtain a solution C with a photoinitiator mass fraction of 3.95%;

[0045] S4: Add solution B dropwise to solution A and stir magnetically at 500 r / min for 10 min to obtain a homogeneous mixed solution D; slowly add solution C to mixed solution D and stir thoroughly, then sonicate for 10 min until uniformly dispersed to obtain solution E; slowly draw solution E into a liquid crystal cell of constant thickness using a capillary tube, polymerize it thoroughly under ultraviolet light for 10 min, and then vacuum dry to obtain the final product, liquid crystal polymer electrolyte.

[0046] Figure 7 The diagram shows the cycle performance of the liquid crystal electrolyte prepared in this embodiment as a lithium-ion battery electrolyte. Figure 7It is evident that this electrode exhibits good cycle stability and high lithium storage capacity, demonstrating excellent electrochemical performance.

[0047] Comparative Example 1: A method for preparing a liquid crystal electrolyte based on polymerizable ionic liquids, comprising the following steps:

[0048] S1: Add lithium bis(trifluoromethanesulfonyl)imide to 1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imide and sonicate for 10 min until completely dissolved to obtain solution A with a lithium salt mass fraction of 6.25%;

[0049] S2: 2-Methyl-1,4-phenylene bis(4-(3-(acryloyloxy)propoxy)benzoate) was heated for 5 minutes under a blower until completely dissolved, and then stirred thoroughly to obtain solution B;

[0050] S3: Add the photoinitiator 1-hydroxycyclohexylphenyl ketone to 2,2'-(ethylenedioxy)diethylthiol and sonicate for 10 min until completely dissolved to obtain a solution C with a photoinitiator mass fraction of 3.95%;

[0051] S4: Add solution B dropwise to solution A and stir magnetically at 500 r / min for 10 min to obtain a homogeneous mixed solution D; slowly add solution C to mixed solution D and stir thoroughly, then sonicate for 10 min until uniformly dispersed to obtain solution E; slowly draw solution E into a liquid crystal cell of constant thickness using a capillary tube, polymerize it thoroughly under ultraviolet light for 10 min, and then vacuum dry to obtain the final product, liquid crystal polymer electrolyte.

[0052] Comparative Example 2: A method for preparing a liquid crystal electrolyte based on polymerizable ionic liquids, comprising the following steps:

[0053] S1: Add lithium bis(trifluoromethanesulfonyl)imide to 1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imide and sonicate for 10 min until completely dissolved to obtain solution A with a lithium salt mass fraction of 6.25%;

[0054] S2: 1-Vinyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is heated under a blower for 5 minutes until completely dissolved, and then stirred thoroughly to obtain solution B;

[0055] S3: Add the photoinitiator 1-hydroxycyclohexylphenyl ketone to 2,2'-(ethylenedioxy)diethylthiol and sonicate for 10 min until completely dissolved to obtain a solution C with a photoinitiator mass fraction of 3.95%;

[0056] S4: Add solution B dropwise to solution A and stir magnetically at 500 r / min for 10 min to obtain a homogeneous mixed solution D; slowly add solution C to mixed solution D and stir thoroughly, then sonicate for 10 min until uniformly dispersed to obtain solution E; slowly draw solution E into a liquid crystal cell of constant thickness using a capillary tube, polymerize it thoroughly under ultraviolet light for 10 min, and then vacuum dry to obtain the final product, liquid crystal polymer electrolyte.

[0057] The polymer in Comparative Example 1 exhibits excessive brittleness and lacks sufficient toughness, making it prone to fracture or breakage under external forces. This brittleness may lead to cracking during processing or fracture when subjected to impact or tension during use, failing to meet the durability requirements of practical applications.

[0058] The polymer in Comparative Example 2 lacks sufficient strength to support the molding process, making it unsuccessful to mold using conventional processing methods. Due to the material's poor mechanical properties, deformation, breakage, or failure to achieve the desired structural requirements may occur during molding.

[0059] Therefore, it is evident that the liquid crystal polymer electrolytes obtained in Comparative Examples 1 and 2 exhibit poor mechanical properties. In contrast, the liquid crystal electrolyte based on polymerizable ionic liquid prepared in the embodiments of this invention is more suitable for applications requiring high stress resistance and long-term use, exhibiting structural stability, high ionic conductivity, a wide electrochemical window, and superior cycling rate performance.

[0060] This invention uses polymerizable ionic liquids and liquid crystal elastomers as the matrix. The polymer network is also filled with lithium salts and ionic liquids, which can promote the transport of lithium ions. After ultraviolet polymerization to form a film, it can further reduce the safety hazards such as leakage and explosion of traditional liquid electrolytes. Using liquid crystal cells of different sizes to form the film can also adjust the thickness of the electrolyte film and achieve different responses to different needs.

[0061] It should be noted that the embodiments described above are merely preferred embodiments of the present invention. For those skilled in the art, various modifications, improvements, and equivalent substitutions can be made to the present invention without departing from its principles, and such modifications, improvements, and equivalent substitutions are also considered to fall within the protection scope of the claims of the present invention.

Claims

1. A method for the preparation of a liquid crystalline electrolyte based on a polymerizable ionic liquid, characterized in that, Comprising the following steps: S1: adding lithium bis(trifluoromethanesulfonimide) into 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl) imide, ultrasonic dispersion to completely dissolved to obtain solution A; S2: mixing 2-methyl-1, 4-phenylene bis(4-(3-(acryloyloxy) propoxy) benzoate) and 1-vinyl-3-methylimidazole bis(trifluoromethanesulfonate) in a molar ratio of 3:1~1:1, heating to completely dissolved and then stirring thoroughly to obtain solution B; S3: adding photoinitiator 1-hydroxycyclohexyl phenone into 2, 2'-(ethylenedioxy) diethyl sulfide, ultrasonic dispersion to completely dissolved to obtain solution C; S4: adding the obtained solution B dropwise into solution A and stirring uniformly to obtain mixed solution D; adding solution C into mixed solution D, stirring thoroughly and then ultrasonic dispersion to obtain solution E; slowly sucking solution E into a liquid crystal cell with constant thickness, vacuum drying after sufficient polymerization under ultraviolet lamp to obtain the final product liquid crystal state electrolyte.

2. The method for producing a polymerizable ionic liquid-based liquid crystalline electrolyte according to claim 1, characterized by, In solution A, the mass fraction of lithium bis(trifluoromethanesulfonimide) is 5~8%.

3. The method for producing a polymerizable ionic liquid-based liquid crystalline electrolyte according to claim 1, characterized by, In solution C, the mass fraction of 1-hydroxycyclohexyl phenone added into 2, 2'-(ethylenedioxy) diethyl sulfide is 5~20%.

4. The method for producing a polymerizable ionic liquid-based liquid crystalline electrolyte according to claim 1, characterized by, The ultrasonic dispersion time in steps S1, S3 and S4 is 10~20 min.

5. The method for preparing a polymerizable ionic liquid-based liquid crystalline electrolyte according to claim 1, characterized by, The stirring in steps S2 and S4 is all magnetic stirring, the stirring speed is 500~700 r / min and the stirring time is 5~10 min.

6. The method of preparing a polymerizable ionic liquid-based liquid crystalline electrolyte according to claim 1, characterized in that, The vacuum drying in step S4 is carried out at 80℃, and the time is 8~12 h.

7. The method of producing a polymerizable ionic liquid-based liquid crystalline electrolyte according to claim 1, characterized by, The intensity of the UV light in step S4 is 100 - 120 mw / cm 2 .

8. A liquid crystalline electrolyte based on a polymerizable ionic liquid, characterized in that, Prepared by the preparation method of the polymerizable ionic liquid-based liquid crystal state electrolyte according to claim 1.

9. Application of the polymerizable ionic liquid-based liquid crystal state electrolyte according to claim 8 in lithium ion battery.

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